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fMRI investigation of cortical and subcortical networks in the learning of abstract and effector-specific representations of motor sequences.

RS Bapi — 2007-02-17T02:13:53-00:00

Neuroimage, Vol. 32, No. 2. (15 August 2006), pp. 714-727.

A visuo-motor sequence can be learned as a series of visuo-spatial cues or as a sequence of effector movements. Earlier imaging studies have revealed that a network of brain areas is activated in the course of motor sequence learning. However, these studies do not address the question of the type of representation being established at various stages of visuo-motor sequence learning. In an earlier behavioral study, we demonstrated that acquisition of visuo-spatial sequence representation enables rapid learning in the early stage and progressive establishment of somato-motor representation helps speedier execution by the late stage. We conducted functional magnetic resonance imaging (fMRI) experiments wherein subjects learned and practiced the same sequence alternately in normal and rotated settings. In one rotated setting (visual), subjects learned a new motor sequence in response to an identical sequence of visual cues as in normal. In another rotated setting (motor), the display sequence was altered as compared to normal, but the same sequence of effector movements was used to perform the sequence. Comparison of different rotated settings revealed analogous transitions both in the cortical and subcortical sites during visuo-motor sequence learning-a transition of activity from parietal to parietal-premotor and then to premotor cortex and a concomitant shift was observed from anterior putamen to a combined activity in both anterior and posterior putamen and finally to posterior putamen. These results suggest a putative role for engagement of different cortical and subcortical networks at various stages of learning in supporting distinct sequence representations.

Influence of predator stress on the consolidation versus retrieval of long-term spatial memory and hippocampal spinogenesis

David Diamond — 2007-06-08T20:08:02-00:00

Hippocampus, Vol. 16, No. 7. (2006), pp. 571-576.

We have studied the influence of predator stress (30 min of cat exposure) on long-term (24 h) spatial memory and the density of spines in basilar dendrites of CA1 neurons. Predator stress occurred either immediately before water maze training (Stress Pre-Training) or before the 24 h memory test (Stress Pre-Retrieval). The Control (nonstress) group exhibited excellent long-term spatial memory and a robust increase in the density of stubby, but not mushroom, shaped spines. The Stress Pre-Training group had impaired long-term memory and did not exhibit any changes in spine density. The Stress Pre-Retrieval group was also impaired in long-term memory performance, but this group exhibited an increase in the density of stubby, but not mushroom, shaped spines, which was indistinguishable from the control group. These findings indicate that: (1) A single day of water maze training under control conditions produced intact long-term memory and an increase in the density of stubby spines in CA1; (2) Stress before training interfered with the consolidation of information into long-term memory and suppressed the training-induced increase in spine density; and (3) Stress immediately before the 24 h memory test trial impaired the retrieval of the stored memory, but did not reverse the training-induced increase in CA1 spine density. Overall, this work provides evidence of structural plasticity in dendrites of CA1 neurons which may be involved in the consolidation process, and how spinogenesis and memory are modulated by stress. © 2006 Wiley-Liss, Inc.

Visual long-term memory for spatial frequency?

Lages — 2006-09-22T22:48:22-00:00

Psychonomic Bulletin & Review, Vol. 13, No. 3. (June 2006), pp. 486-492.

Dynamic Shifts of Limited Working Memory Resources in Human Vision

Paul Bays — 2008-08-08T14:47:15-00:00

Science, Vol. 321, No. 5890. (8 August 2008), pp. 851-854.

Our ability to remember what we have seen is very limited. Most current views characterize this limit as a fixed number of items--only four objects--that can be held in visual working memory. We show that visual memory capacity is not fixed by the number of objects, but rather is a limited resource that is shared out dynamically between all items in the visual scene. This resource can be shifted flexibly between objects, with allocation biased by selective attention and toward targets of upcoming eye movements. The proportion of resources allocated to each item determines the precision with which it is remembered, a relation that we show is governed by a simple power law, allowing quantitative estimates of resource distribution in a scene. 10.1126/science.1158023

Perirhinal and hippocampal contributions to visual recognition memory can be distinguished from those of occipito-temporal structures based on conscious awareness of prior occurrence

SL Danckert — 2007-09-26T22:10:28-00:00

Hippocampus, Vol. 9999, No. 9999. (2007), NA.

The ability of humans to distinguish consciously between new and previously encountered objects can be probed with visual recognition memory tasks that require explicit old-new discriminations. Medial temporal-lobe (MTL) lesions impair performance on such tasks. Within the MTL, both perirhinal cortex and the hippocampus have been implicated. Cognitive processes can also be affected by past object encounters in the absence of conscious recognition, as in repetition priming tasks. Past functional neuroimaging findings in healthy individuals suggest that even in tasks that require conscious recognition decisions for visual stimuli, posterior cortical structures in the ventral visual pathway distinguish between old and new objects at a nonconscious level. Conclusive evidence that differentiates the neural underpinnings of conscious from nonconscious processes in recognition memory, however, is still missing. In particular, functional magnetic resonance imaging (fMRI) findings for the MTL have been inconsistent towards this end. In the present fMRI study, we tested whether perirhinal and hippocampal contributions to recognition memory can be distinguished from those of occipito-temporal structures in the ventral visual pathway based on the participants' reported conscious awareness of prior occurrence. Images of objects with a large degree of feature overlap served as stimuli; they were selected to ensure an involvement of perirhinal cortex in the present recognition task, based on evidence from past lesion-based research. We found that both perirhinal cortex and occipito-temporal cortex showed a differential old-new response that reflected a repetition-related decrease in activity (i.e., new > old). Whereas in perirhinal cortex this decrease was observed with respect to whether subjects reported objects to be old or new, irrespective of the true item status, in occipito-temporal cortex it occurred in relation to whether objects were truly old or new, irrespective of the participants' conscious reports. Hippocampal responses differed in their exact pattern from those of perirhinal cortex, but were also related to the conscious recognition reports. These results indicate that both perirhinal and hippocampal contributions can be distinguished from those of occipito-temporal structures in the ventral visual pathway based on the participants' reported conscious awareness of prior occurrence. © 2007 Wiley-Liss, Inc.

Discrete fixed-resolution representations in visual working memory

Weiwei Zhang — 2008-04-03T16:42:31-00:00

Nature (02 April 2008)

Spontaneous navigational strategies and performance in the virtual town.

Nicole Etchamendy — 2007-06-10T04:24:01-00:00

Hippocampus (1 June 2007)

The 4-on-8 virtual maze provides evidence for variability in spontaneous strategy use during navigation. Functional magnetic resonance imaging (MRI) confirmed that these spatial and response strategies rely on the hippocampus and caudate nucleus memory systems, respectively. We asked whether the spontaneous use of a particular navigational strategy was associated with a particular ability to navigate in one's environment. We tested 30 young participants on the 4-on-8 virtual maze and we assessed their way finding ability in a virtual town. As expected, spatial learners performed well in the virtual town and the response learners, who never used external landmarks and relied purely on an egocentric strategy, performed poorly. Interestingly, a group who used the most efficient response strategy based on external landmarks in the 4-on-8 virtual maze, switched to the most efficient spatial strategy in the virtual town. Our data suggest that the best navigators are those who appropriately use spatial or response strategies depending on the demands of the task. (c) 2007 Wiley-Liss, Inc.

Contrasting roles of neural firing rate and local field potentials in human memory.

Arne Ekstrom — 2007-06-10T04:23:31-00:00

Hippocampus (1 June 2007)

Recording the activity of neurons is a mainstay of animal memory research, while human recordings are generally limited to the activity of large ensembles of cells. The relationship between ensemble activity and neural firing rate during declarative memory processes, however, remains unclear. We recorded neurons and local field potentials (LFPs) simultaneously from the same sites in the human hippocampus and entorhinal cortex (ERC) in patients with implanted intracranial electrodes during a virtual taxi-driver task that also included a memory retrieval component. Neurons increased their firing rate in response to specific passengers or landmarks both during navigation and retrieval. Although we did not find item specificity in the broadband LFP, both theta- and gamma-band LFPs increased power to specific items on a small but significant percent of channels. These responses, however, did not correlate with item-specific neural responses. To contrast item-specific responses with process-specific responses during memory, we compared neural and LFP responses during encoding (navigation) and retrieval (associative and item-specific recognition). A subset of neurons also altered firing rates nonspecifically while subjects viewed items during encoding. Interestingly, LFPs in the hippocampus and ERC increased in power nonspecifically while subjects viewed items during retrieval, more often during associative than item-recognition. Furthermore, we found no correlation between neural firing rate and broadband, theta-band, and gamma-band LFPs during process-specific responses. Our findings suggest that neuronal firing and ensemble activity can be dissociated during encoding, item-maintenance, and retrieval in the human hippocampal area, likely relating to functional properties unique to this region. (c) 2007 Wiley-Liss, Inc.

Control of sensorimotor variability by consequences

Laurent Madelain — 2007-08-31T16:01:41-00:00

J Neurophysiol (15 August 2007), 01286.2006.

Studies of reaction time distributions provide a useful quantitative approach to understand decision processes at the neural level and at the behavioral level. A strong relationship between the spread of latencies and the median is generally accepted even though there has been no attempt to disentangle experimentally these two parameters. Here we test the ability to independently control the median and the variability in reaction times. Reaction times were measured in human subjects instructed to make a discrimination between a target and a distractor in a 2AFC task. In a first experiment, saccadic latencies were measured. In a second experiment, we used manual response reaction times. Subjects were trained to produce four different reaction time distributions. A reinforcing feedback was given depending on both the variability and the median of the latency distributions. When low variability was reinforced the standard deviation of reaction time distributions were reduced by a factor of two and when high variability was reinforced, the standard deviation returned to baseline level. Our procedure independently affected the spread and the median of the distribution patterns. By fitting the latency distributions using the Reddi and Carpenter LATER model, we found that these effects could be simulated by changing the distribution of the noise affecting the decision process. Our results demonstrate that learned contingencies can affect reaction time variability and support the view that the so-called noise level in decision processes can undergo long-term changes. 10.1152/jn.01286.2006

Brain areas selective for both observed and executed movements

Ilan Dinstein — 2007-08-31T15:57:25-00:00

J Neurophysiol (27 June 2007), 00238.2007.

When observing a particular movement a subset of movement-selective visual and visuomotor neurons are active in the brain of the observer forming a representation of the observed movement. Similarly, when executing a movement a subset of movement-selective motor and visuomotor neurons are active forming a representation of the executed movement. In this study we used an fMRI-adaptation protocol to assess cortical response selectivity to observed and executed movements simultaneously. Subjects freely played the rock-paper-scissors game against a videotaped opponent, sometimes repeatedly observing or executing the same movement on subsequent trials. Numerous brain areas exhibited adaptation (repetition suppression) during either repeated observations or repeated executions of the same movement. A subset of areas exhibited an overlap of both effects, containing neurons with selective responses for both executed and observed movements. We describe the function of these unique movement representation areas in the context of the human mirror system, which is expected to respond selectively to both observed and executed movements. 10.1152/jn.00238.2007

The Promise of Parallel Universes

Greg Miller — 2007-09-08T16:44:29-00:00

Science, Vol. 317, No. 5842. (7 September 2007), pp. 1341-1343.

10.1126/science.317.5842.1341

Familiarity and Conceptual Priming Engage Distinct Cortical Networks

Joel Voss — 2007-12-04T14:44:07-00:00

Cereb. Cortex (1 December 2007), bhm200.

Familiarity refers to an explicit recognition experience without any necessary retrieval of specific detail related to the episode during which initial learning transpired. Prior experience can also implicitly influence subsequent processing through a memory phenomenon termed conceptual priming, which occurs without explicit awareness of recognition. Resolving current theoretical controversy on relationships between familiarity and conceptual priming requires a clarification of their neural substrates. Accordingly, we obtained functional magnetic resonance images in a novel paradigm for separately assessing neural correlates of familiarity and conceptual priming using famous and nonfamous faces. Conceptual priming, as shown by more accurate behavioral responses to strongly conceptually primed than to weakly conceptually primed faces, was associated with activity reductions in left prefrontal cortex, whereas familiarity was associated with activity enhancements in right parietal cortex for more-familiar compared with less-familiar faces. This neuroimaging evidence implicates separate neurocognitive processes operative in explicit stimulus recognition versus implicit conceptual priming. 10.1093/cercor/bhm200

Visual Quality Determines the Direction of Neural Repetition Effects

Turk-Browne — 2007-01-05T22:18:35-00:00

Cerebral Cortex, Vol. 17, No. 2. (February 2007), pp. 425-433.

Environmental novelty is signaled by reduction of the hippocampal theta frequency.

A Jeewajee — 2007-12-23T17:39:39-00:00

Hippocampus (14 December 2007)

The hippocampal formation (HF) plays a key role in novelty detection, but the mechanisms remain unknown. Novelty detection aids the encoding of new information into memory-a process thought to depend on the HF and to be modulated by the theta rhythm of EEG. We examined EEG recorded in the HF of rats foraging for food within a novel environment, as it became familiar over the next five days, and in two more novel environments unexpectedly experienced in trials interspersed with familiar trials over three further days. We found that environmental novelty produces a sharp reduction in the theta frequency of foraging rats, that this reduction is greater for an unexpected environment than for a completely novel one, and that it slowly disappears with increasing familiarity. These results do not reflect changes in running speed and suggest that the septo-hippocampal system signals unexpected environmental change via a reduction in theta frequency. In addition, they provide evidence in support of a cholinergically mediated mechanism for novelty detection, have important implications for our understanding of oscillatory coding within memory and for the interpretation of event-related potentials, and provide indirect support for the oscillatory interference model of grid cell firing in medial entorhinal cortex. (c) 2007 Wiley-Liss, Inc.

Tuned Responses of Astrocytes and Their Influence on Hemodynamic Signals in the Visual Cortex

James Schummers — 2008-06-20T10:31:33-00:00

Science, Vol. 320, No. 5883. (20 June 2008), pp. 1638-1643.

Astrocytes have long been thought to act as a support network for neurons, with little role in information representation or processing. We used two-photon imaging of calcium signals in the ferret visual cortex in vivo to discover that astrocytes, like neurons, respond to visual stimuli, with distinct spatial receptive fields and sharp tuning to visual stimulus features including orientation and spatial frequency. The stimulus-feature preferences of astrocytes were exquisitely mapped across the cortical surface, in close register with neuronal maps. The spatially restricted stimulus-specific component of the intrinsic hemodynamic mapping signal was highly sensitive to astrocyte activation, indicating that astrocytes have a key role in coupling neuronal organization to mapping signals critical for noninvasive brain imaging. Furthermore, blocking astrocyte glutamate transporters influenced the magnitude and duration of adjacent visually driven neuronal responses. 10.1126/science.1156120

Cortical Neuronal Responses to Optic Flow Are Shaped by Visual Strategies for Steering

William Page — 2007-07-13T18:37:04-00:00

Cereb. Cortex (9 July 2007), bhm109.

We hypothesized that neuronal responses to virtual self-movement would be enhanced during steering tasks. We recorded the activity of medial superior temporal (MSTd) neurons in monkeys trained to steer a straight-ahead course, using optic flow. We found smaller optic flow responses during active steering than during the passive viewing of the same stimuli. Behavioral analysis showed that the monkeys had learned to steer using local motion cues. Retraining the monkeys to use the global pattern of optic flow reversed the effects of the active-steering task: active steering then evoked larger responses than passive viewing. We then compared the responses of neurons during active steering by local motion and by global patterns: Local motion trials promoted the use of local dot movement near the center of the stimulus by occluding the peripheral visual field midway through the trial. Global pattern trials promoted the use of radial pattern movement by occluding the central visual field midway through the trial. In this study, identical full-field optic-flow stimuli evoked larger responses in global-pattern trials than in local motion trials. We conclude that the selection of specific visual cues reflects strategies for active steering and alters MSTd neuronal responses to optic flow. 10.1093/cercor/bhm109

Patches with Links: A Unified System for Processing Faces in the Macaque Temporal Lobe

Sebastian Moeller — 2008-06-06T00:40:10-00:00

Science, Vol. 320, No. 5881. (6 June 2008), pp. 1355-1359.

The brain processes objects through a series of regions along the ventral visual pathway, but the circuitry subserving the analysis of specific complex forms remains unknown. One complex form category, faces, selectively activates six patches of cortex in the macaque ventral pathway. To identify the connectivity of these face patches, we used electrical microstimulation combined with simultaneous functional magnetic resonance imaging. Stimulation of each of four targeted face patches produced strong activation, specifically within a subset of the other face patches. Stimulation outside the face patches produced an activation pattern that spared the face patches. These results suggest that the face patches form a strongly and specifically interconnected hierarchical network. 10.1126/science.1157436

A general area theorem for the samedifferent paradigm

Micheyl — 2008-06-24T08:05:58-00:00

Perception & Psychophysics, Vol. 70, No. 5. (July 2008), pp. 761-764.

Perceived object trajectories during occlusion constrain visual statistical learning.

J Fiser — 2008-07-11T19:15:37-00:00

Psychonomic bulletin & review, Vol. 14, No. 1. (February 2007), pp. 173-178.

Visual statistical learning of shape sequences was examined in the context of occluded object trajectories. In a learning phase, participants viewed a sequence of moving shapes whose trajectories and speed profiles elicited either a bouncing or a streaming percept: The sequences consisted of a shape moving toward and then passing behind an occluder, after which two different shapes emerged from behind the occluder. At issue was whether statistical learning linked both object transitions equally, or whether the percept of either bouncing or streaming constrained the association between pre- and postocclusion objects. In familiarity judgments following the learning, participants reliably selected the shape pair that conformed to the bouncing or streaming bias that was present during the learning phase. A follow-up experiment demonstrated that differential eye movements could not account for this finding. These results suggest that sequential statistical learning is constrained by the spatiotemporal perceptual biases that bind two shapes moving through occlusion, and that this constraint thus reduces the computational complexity of visual statistical learning.

Neural Resources Associated with Perceptual Judgment across Sensory Modalities.

Joong Nam Yang — 2007-04-10T17:52:08-00:00

Cereb Cortex (5 April 2007)

Electrophysiological and brain imaging studies have shown that different populations of neurons contribute to perceptual decision making. Perceptual judgment is a complicated process that has several subprocesses, including the final step of a discrete choice among available possibilities. Using the psychophysical paradigm of difference scaling combined with functional magnetic resonance imaging, we identify an area within a distributed representation that is consistently invoked in perceptual decision. Difference judgments based on visual (color, form, and motion) cues and auditory cues show that a population of neurons in the posterior banks of the intraparietal sulcus (PIPS) is consistently activated for perceptual judgment across visual attributes and sensory modalities, suggesting that those neurons in PIPS are associated with perceptual judgment.

Auditory Change Detection: Simple Sounds Are Not Memorized Better Than Complex Sounds

Laurent Demany — 2007-12-28T00:26:41-00:00

Psychological Science, Vol. 19, No. 1. (2008), pp. 85-91.

ABSTRACT- Previous research has shown that the detectability of a local change in a visual image is essentially independent of the complexity of the image when the interstimulus interval (ISI) is very short, but is limited by a low-capacity memory system when the ISI exceeds 100 ms. In the study reported here, listeners made same/different judgments on pairs of successive "chords" (sums of pure tones with random frequencies). The change to be detected was always a frequency shift in one of the tones, and which tone would change was unpredictable. Performance worsened as the number of tones increased, but this effect was not larger for 2-s ISIs than for 0-ms ISIs. Similar results were obtained when a chord was followed by a single tone that had to be judged as higher or lower than the closest component of the chord. Overall, our data suggest that change detection is based on different mechanisms in audition and vision.

Stress modulates the use of spatial versus stimulus-response learning strategies in humans

Lars Schwabe — 2007-06-08T20:12:29-00:00

Learn. Mem., Vol. 14, No. 1. (1 January 2007), pp. 109-116.

Animal studies provided evidence that stress modulates multiple memory systems, favoring caudate nucleus-based "habit" memory over hippocampus-based "cognitive" memory. However, effects of stress on learning strategy and memory consolidation were not differentiated. We specifically address the effects of psychosocial stress on the applied learning strategy in humans. We designed a spatial learning task that allowed differentiating spatial from stimulus-response learning strategies during acquisition. In 13 subsequent trials, participants (88 male and female students) had to locate a "win" card out of four placed at a fixed location in a 3D model of a room. Relocating one cue in the last trial allowed inferring the applied learning strategy. Half of them participated first in the "Trier Social Stress Test." Salivary cortisol and heart rate measurements were taken. Stressed participants used a stimulus-response strategy significantly more often than controls. Subsequent verbal report revealed that spatial learners had a more complete awareness of response options than stimulus-response learners. Importantly, learning performance was not affected by stress. Taken together, stress prior to learning facilitated simple stimulus-response learning strategies in humans--at the expense of a more cognitive learning strategy. Depending on the context, we consider this as an adaptive response. 10.1101/lm.435807

Sample Size Planning for Statistical Power and Accuracy in Parameter Estimation.

Scott E Maxwell — 2008-01-01T09:51:09-00:00

Annu Rev Psychol, Vol. 59 (10 January 2008), pp. 537-563.

This review examines recent advances in sample size planning, not only from the perspective of an individual researcher, but also with regard to the goal of developing cumulative knowledge. Psychologists have traditionally thought of sample size planning in terms of power analysis. Although we review recent advances in power analysis, our main focus is the desirability of achieving accurate parameter estimates, either instead of or in addition to obtaining sufficient power. Accuracy in parameter estimation (AIPE) has taken on increasing importance in light of recent emphasis on effect size estimation and formation of confidence intervals. The review provides an overview of the logic behind sample size planning for AIPE and summarizes recent advances in implementing this approach in designs commonly used in psychological research.

Melanopsin cells are the principal conduits for rod–cone input to non-image-forming vision

Ali Güler — 2008-04-24T18:14:00-00:00

Nature (23 April 2008)

Which computational mechanisms operate in the hippocampus during novelty detection?

Dharshan Kumaran — 2007-07-01T00:51:36-00:00

Hippocampus (27 June 2007)

A fundamental property of adaptive behavior is the ability to rapidly distinguish what is novel from what is familiar in our environment. Empirical evidence and computational work have provided biologically plausible models of the neural substrate and mechanisms underlying the coding of stimulus novelty in the perirhinal cortex. In this article, we highlight the importance of a different category of novelty, namely associative novelty, which has received relatively little attention, despite its clear ecological importance. While previous studies in both animals and humans have documented hippocampal responses in relation to associative novelty, a key issue concerning the computations underlying these novelty signals has not been previously addressed. We argue that this question has importance not only for our understanding of novelty processing, but also for advancing our knowledge of the fundamental computational operations performed by the hippocampus. We suggest a different approach to this problem, and discuss recent evidence supporting the hypothesis that the hippocampus operates as a comparator during the processing of associative novelty, generating mismatch/novelty signals when prior predictions are violated by sensory reality. We also draw on conceptual similarities between associative novelty and contextual novelty to suggest that empirical findings from these two seemingly distant research fields accord with the operation of a comparator mechanism during novelty detection more generally. We therefore conclude that a comparator mechanism may underlie the role of the hippocampus not only in detecting occurrences that are unexpected given specific associatively retrieved predictions, but also events that violate more abstract properties of the experimental context. (c) 2007 Wiley-Liss, Inc.

The coming acceleration of global population ageing

Wolfgang Lutz — 2008-01-20T18:12:47-00:00

Nature (20 January 2008)

Activating the Medial Temporal Lobe during Oddity Judgment for Faces and Scenes

Andy Lee — 2007-07-06T15:34:19-00:00

Cereb. Cortex (5 July 2007), bhm104.

Impairments in visual discrimination beyond long-term declarative memory have been found in amnesic individuals, with hippocampal lesions resulting in deficits in scene discrimination and perirhinal cortex damage affecting object discrimination. To complement these findings, the present functional magnetic resonance imaging study found that in healthy participants oddity judgment for novel trial-unique scenes, compared with face or size oddity, was associated with increased posterior hippocampus and parahippocampal cortex activity. In contrast, perirhinal and anterior hippocampus activity was observed during unfamiliar trial-unique face oddity judgment, when contrasted with scene or size oddity tasks. Activity in all of these regions decreased as the stimuli were repeated across trials, reflecting the participants' increasing familiarity with the stimuli. This change was significant in all areas, with the exception of the perirhinal cortex, right anterior hippocampus, and to a lesser extent the left anterior hippocampus during face oddity judgment. One possibility is that the activity in these regions may not reflect entirely episodic memory encoding but, in part, processes beyond the mnemonic domain. Thus, the perirhinal cortex, and possibly anterior hippocampus, may play a more generic role in the discrimination and processing of objects. 10.1093/cercor/bhm104

The Biological Basis of Audition

Gregg Recanzone — 2008-03-14T14:16:57-00:00

Annual Review of Psychology, Vol. 59, No. 1. (2008), pp. 119-142.

Interest has recently surged in the neural mechanisms of audition, particularly with regard to functional imaging studies in human subjects. This review emphasizes recent work on two aspects of auditory processing. The first explores auditory spatial processing and the role of the auditory cortex in both nonhuman primates and human subjects. The interactions with visual stimuli, the ventriloquism effect, and the ventriloquism aftereffect are also reviewed. The second aspect is temporal processing. Studies investigating temporal integration, forward masking, and gap detection are reviewed, as well as examples from the birdsong system and echolocating bats.

Visual Perception and the Statistical Properties of Natural Scenes

Wilson Geisler — 2008-03-14T14:15:11-00:00

Annual Review of Psychology, Vol. 59, No. 1. (2008), pp. 167-192.

The environments in which we live and the tasks we must perform to survive and reproduce have shaped the design of our perceptual systems through evolution and experience. Therefore, direct measurement of the statistical regularities in natural environments (scenes) has great potential value for advancing our understanding of visual perception. This review begins with a general discussion of the natural scene statistics approach, of the different kinds of statistics that can be measured, and of some existing measurement techniques. This is followed by a summary of the natural scene statistics measured over the past 20 years. Finally, there is a summary of the hypotheses, models, and experiments that have emerged from the analysis of natural scene statistics.

The Mind and Brain of Short-Term Memory

John Jonides — 2008-03-14T14:13:41-00:00

Annual Review of Psychology, Vol. 59, No. 1. (2008), pp. 193-224.

The past 10 years have brought near-revolutionary changes in psychological theories about short-term memory, with similarly great advances in the neurosciences. Here, we critically examine the major psychological theories (the mind) of short-term memory and how they relate to evidence about underlying brain mechanisms. We focus on three features that must be addressed by any satisfactory theory of short-term memory. First, we examine the evidence for the architecture of short-term memory, with special attention to questions of capacity and how--or whether--short-term memory can be separated from long-term memory. Second, we ask how the components of that architecture enact processes of encoding, maintenance, and retrieval. Third, we describe the debate over the reason about forgetting from short-term memory, whether interference or decay is the cause. We close with a conceptual model tracing the representation of a single item through a short-term memory task, describing the biological mechanisms that might support psychological processes on a moment-by-moment basis as an item is encoded, maintained over a delay with some forgetting, and ultimately retrieved.

Quantal noise from human red cone pigment

Yingbin Fu — 2008-04-26T06:19:24-00:00

Nature Neuroscience, Vol. 11, No. 5. (20 April 2008), pp. 565-571.

In the Footsteps of Biological Motion and Multisensory Perception: Judgments of Audiovisual Temporal Relations Are Enhanced for Upright Walkers

Saygin — 2008-05-12T23:10:54-00:00

Psychological Science, Vol. 19, No. 5. (May 2008), pp. 469-475.

Relativity of Remembering: Why the Laws of Memory Vanished

Henry — 2008-03-14T14:12:13-00:00

Annual Review of Psychology, Vol. 59, No. 1. (2008), pp. 225-254.

For 120 years, cognitive psychologists have sought general laws of learning and memory. In this review I conclude that none has stood the test of time. No empirical law withstands manipulation across the four sets of factors that Jenkins (1979) identified as critical to memory experiments: types of subjects, kinds of events to be remembered, manipulation of encoding conditions, and variations in test conditions. Another factor affecting many phenomena is whether a manipulation of conditions occurs in randomized, within-subjects designs rather than between-subjects (or within-subject, blocked) designs. The fact that simple laws do not hold reveals the complex, interactive nature of memory phenomena. Nonetheless, the science of memory is robust, with most findings easily replicated under the same conditions as originally used, but when other variables are manipulated, effects may disappear or reverse. These same points are probably true of psychological research in most, if not all, domains.

How persuasive is a good fit? A comment on theory testing.

S Roberts — 2008-07-02T19:11:07-00:00

Psychological review, Vol. 107, No. 2. (April 2000), pp. 358-367.

Quantitative theories with free parameters often gain credence when they closely fit data. This is a mistake. A good fit reveals nothing about the flexibility of the theory (how much it cannot fit), the variability of the data (how firmly the data rule out what the theory cannot fit), or the likelihood of other outcomes (perhaps the theory could have fit any plausible result), and a reader needs all 3 pieces of information to decide how much the fit should increase belief in the theory. The use of good fits as evidence is not supported by philosophers of science nor by the history of psychology; there seem to be no examples of a theory supported mainly by good fits that has led to demonstrable progress. A better way to test a theory with free parameters is to determine how the theory constrains possible outcomes (i.e., what it predicts), assess how firmly actual outcomes agree with those constraints, and determine if plausible alternative outcomes would have been inconsistent with the theory, allowing for the variability of the data.

Neural Representation of Navigational Relevance Is Rapidly Induced and Long Lasting.

Gabriele Janzen — 2006-11-22T19:58:02-00:00

Cereb Cortex (29 June 2006)

Successful navigation is facilitated by the presence of landmarks. Previous functional magnetic resonance imaging (fMRI) evidence indicated that the human parahippocampal gyrus automatically distinguishes between landmarks placed at navigationally relevant (decision points) and irrelevant locations (nondecision points). This storage of navigational relevance can provide a neural mechanism underlying successful navigation. However, an efficient wayfinding mechanism requires that important spatial information is learned quickly and maintained over time. The present study investigates whether the representation of navigational relevance is modulated by time and practice. Participants learned 2 film sequences through virtual mazes containing objects at decision and at nondecision points. One maze was shown one time, and the other maze was shown 3 times. Twenty-four hours after study, event-related fMRI data were acquired during recognition of the objects. The results showed that activity in the parahippocampal gyrus was increased for objects previously placed at decision points as compared with objects placed at nondecision points. The decision point effect was not modulated by the number of exposures to the mazes and independent of explicit memory functions. These findings suggest a persistent representation of navigationally relevant information, which is stable after only one exposure to an environment. These rapidly induced and long-lasting changes in object representation provide a basis for successful wayfinding.

For Efficient Navigational Search, Humans Require Full Physical Movement, but Not a Rich Visual Scene

Ruddle — 2006-06-07T16:45:38-00:00

Psychological Science, Vol. 17, No. 6. (June 2006), pp. 460-465.

Synaptic Theory of Working Memory

Gianluigi Mongillo — 2008-03-14T12:03:46-00:00

Science, Vol. 319, No. 5869. (14 March 2008), pp. 1543-1546.

It is usually assumed that enhanced spiking activity in the form of persistent reverberation for several seconds is the neural correlate of working memory. Here, we propose that working memory is sustained by calcium-mediated synaptic facilitation in the recurrent connections of neocortical networks. In this account, the presynaptic residual calcium is used as a buffer that is loaded, refreshed, and read out by spiking activity. Because of the long time constants of calcium kinetics, the refresh rate can be low, resulting in a mechanism that is metabolically efficient and robust. The duration and stability of working memory can be regulated by modulating the spontaneous activity in the network. 10.1126/science.1150769

Human fear-related motor neurocircuitry

T Butler — 2007-12-07T18:12:07-00:00

Neuroscience, Vol. 150, No. 1. (30 November 2007), pp. 1-7.

Using functional magnetic resonance imaging and an experimental paradigm of instructed fear, we observed a striking pattern of decreased activity in primary motor cortex with increased activity in dorsal basal ganglia during anticipation of aversive electrodermal stimulation in 42 healthy participants. We interpret this pattern of activity in motor neurocircuitry in response to cognitively-induced fear in relation to evolutionarily-conserved responses to threat that may be relevant to understanding normal and pathological fear in humans.

Emerging perspectives on emotion-cognition interactions

Kevin Ochsner — 2007-09-19T20:12:28-00:00

Trends in Cognitive Sciences, Vol. 11, No. 8. (August 2007), pp. 317-318.

Developing a cortex specialized for face perception

Cohen — 2007-09-19T20:08:34-00:00

Trends in Cognitive Sciences, Vol. 11, No. 9. (September 2007), pp. 367-369.

Recent developmental functional magnetic resonance imaging studies provide evidence that the cortical specialization for face perception observed in adults emerges only gradually over the first decade of childhood. These developmental results provide a middle-ground view on the long-standing debate in the literature from adults about the specificity or otherwise of face-sensitive areas of cortex. According to this developmental perspective, certain cortical regions become specialized for face perception in adults, partly as a result of a decade or more of experience and partly as a result of initial biases.

Temporal Characteristics of Top-Down Modulations during Working Memory Maintenance: An Event-related Potential Study of the N170 Component.

KK Sreenivasan — 2007-11-06T15:14:10-00:00

J Cogn Neurosci, Vol. 19, No. 11. (November 2007), pp. 1836-1844.

Abstract We investigated the top-down influence of working memory (WM) maintenance on feedforward perceptual processing within occipito-temporal face processing structures. During event-related potential (ERP) recordings, subjects performed a delayed-recognition task requiring WM maintenance of faces or houses. The face-sensitive N170 component elicited by delay-spanning task-irrelevant grayscale noise probes was examined. If early feedforward perceptual activity is biased by maintenance requirements, the N170 ERP component elicited by probes should have a greater N170 amplitude response during face relative to house WM trials. Consistent with this prediction, N170 elicited by probes presented at the beginning, middle, and end of the delay interval was greater in amplitude during face relative to house WM. Thus, these results suggest that WM maintenance demands may modulate early feedforward perceptual processing for the entirety of the delay duration. We argue based on these results that temporally early biasing of domain-specific perceptual processing may be a critical mechanism by which WM maintenance is achieved.

Reduction in white matter connectivity, revealed by diffusion tensor imaging, may account for age-related changes in face perception.

C Thomas — 2008-02-27T18:31:13-00:00

J Cogn Neurosci, Vol. 20, No. 2. (February 2008), pp. 268-284.

An age-related decline in face processing, even under conditions in which learning and memory are not implicated, has been well documented, but the mechanism underlying this perceptual alteration remains unknown. Here, we examine whether this behavioral change may be accounted for by a reduction in white matter connectivity with age. To this end, we acquired diffusion tensor imaging data from 28 individuals aged 18 to 86 years and quantified the number of fibers, voxels, and fractional anisotropy of the two major tracts that pass through the fusiform gyrus, the pre-eminent face processing region in the ventral temporal cortex. We also measured the ability of a subset of these individuals to make fine-grained discriminations between pairs of faces and between pairs of cars. There was a significant reduction in the structural integrity of the inferior fronto-occipital fasciculus (IFOF) in the right hemisphere as a function of age on all dependent measures and there were also some changes in the left hemisphere, albeit to a lesser extent. There was also a clear age-related decrement in accuracy of perceptual discrimination, especially for more challenging perceptual discriminations, and this held to a greater degree for faces than for cars. Of greatest relevance, there was a robust association between the reduction of IFOF integrity in the right hemisphere and the decline in face perception, suggesting that the alteration in structural connectivity between the right ventral temporal and frontal cortices may account for the age-related difficulties in face processing.

Early Face Processing Specificity: It's in the Eyes!

RJ Itier — 2007-11-06T14:56:42-00:00

J Cogn Neurosci, Vol. 19, No. 11. (November 2007), pp. 1815-1826.

Abstract Unlike most other objects that are processed analytically, faces are processed configurally. This configural processing is reflected early in visual processing following face inversion and contrast reversal, as an increase in the N170 amplitude, a scalp-recorded event-related potential. Here, we show that these face-specific effects are mediated by the eye region. That is, they occurred only when the eyes were present, but not when eyes were removed from the face. The N170 recorded to inverted and negative faces likely reflects the processing of the eyes. We propose a neural model of face processing in which face- and eye-selective neurons situated in the superior temporal sulcus region of the human brain respond differently to the face configuration and to the eyes depending on the face context. This dynamic response modulation accounts for the N170 variations reported in the literature. The eyes may be central to what makes faces so special.

How negative emotion enhances the visual specificity of a memory.

EA Kensinger — 2007-11-06T14:53:09-00:00

J Cogn Neurosci, Vol. 19, No. 11. (November 2007), pp. 1872-1887.

Abstract Some studies have suggested that emotion primarily increases memory for "gist," and does not enhance memory for detail. There are, however, some instances in which negative objects (e.g., snake, grenade) are remembered with more visual detail than neutral objects (e.g., barometer, blender). In the present functional magnetic resonance imaging (fMRI) study, we examined the encoding processes that lead a person to remember the exact visual details of negative and neutral objects, and to remember which of two decisions were made about the objects (a size decision or an animacy decision). The enhancement in memory for a negative item's visual details appeared to result from enhanced visual processing: The right fusiform gyrus, a region known to be critical for processing exemplar-specific details, showed a greater extent and magnitude of activity during the successful encoding of negative objects. Activity in the right amygdala also corresponded with memory for visual detail, although it did not relate to memory for the task performed with the item. These data provide strong evidence that engagement of some amygdalar regions can correspond with enhanced memory for certain types of details, but does not ensure successful encoding of all contextual details.

The role of the right prefrontal cortex in self-evaluation of the face: a functional magnetic resonance imaging study.

T Morita — 2008-02-27T18:21:40-00:00

J Cogn Neurosci, Vol. 20, No. 2. (February 2008), pp. 342-355.

Individuals can experience negative emotions (e.g., embarrassment) accompanying self-evaluation immediately after recognizing their own facial image, especially if it deviates strongly from their mental representation of ideals or standards. The aim of this study was to identify the cortical regions involved in self-recognition and self-evaluation along with self-conscious emotions. To increase the range of emotions accompanying self-evaluation, we used facial feedback images chosen from a video recording, some of which deviated significantly from normal images. In total, 19 participants were asked to rate images of their own face (SELF) and those of others (OTHERS) according to how photogenic they appeared to be. After scanning the images, the participants rated how embarrassed they felt upon viewing each face. As the photogenic scores decreased, the embarrassment ratings dramatically increased for the participant's own face compared with those of others. The SELF versus OTHERS contrast significantly increased the activation of the right prefrontal cortex, bilateral insular cortex, anterior cingulate cortex, and bilateral occipital cortex. Within the right prefrontal cortex, activity in the right precentral gyrus reflected the trait of awareness of observable aspects of the self; this provided strong evidence that the right precentral gyrus is specifically involved in self-face recognition. By contrast, activity in the anterior region, which is located in the right middle inferior frontal gyrus, was modulated by the extent of embarrassment. This finding suggests that the right middle inferior frontal gyrus is engaged in self-evaluation preceded by self-face recognition based on the relevance to a standard self.

The Representation of Parts and Wholes in Face-selective Cortex.

Alison Harris — 2008-01-22T15:40:46-00:00

J Cogn Neurosci (17 January 2008)

Abstract Although face perception is often characterized as depending on holistic, rather than part-based, processing, there is behavioral evidence for independent representations of face parts. Although recent work has linked "face-selective" regions defined with functional magnetic resonance imaging (fMRI) to holistic processing, the response of these areas to face parts remains unclear. Here we examine part-based versus holistic processing in "face-selective" visual areas using face stimuli manipulated in binocular disparity to appear either behind or in front of a set of stripes [Nakayama, K., Shimojo, S., & Silverman, G. H. Stereoscopic depth: Its relation to image segmentation, grouping, and the recognition of occluded objects. Perception, 18, 55-68, 1989]. Although the first case will be "filled in" by the visual system and perceived holistically, we demonstrate behaviorally that the latter cannot be completed amodally, and thus, is perceived as parts. Using these stimuli in fMRI, we found significant responses to both depth manipulations in inferior occipital gyrus and middle fusiform gyrus (MFG) "face-selective" regions, suggesting that neural populations in these areas encode both parts and wholes. In comparison, applying these depth manipulations to control stimuli (alphanumeric characters) elicited much smaller signal changes within face-selective regions, indicating that the part-based representation for faces is separate from that for objects. The combined adaptation data also showed an interaction of depth and familiarity within the right MFG, with greater adaptation in the back (holistic) condition relative to parts for familiar but not unfamiliar faces. Together, these data indicate that face-selective regions of the occipito-temporal cortex engage in both part-based and holistic processing. The relative recruitment of such representations may be additionally influenced by external factors such as familiarity.

Cholinergic Enhancement Eliminates Modulation of Neural Activity by Task Difficulty in the Prefrontal Cortex during Working Memory.

Maura L Furey — 2008-02-27T18:09:37-00:00

J Cogn Neurosci (19 February 2008)

Abstract Previously, we demonstrated that enhancing cholinergic activity during a working memory (WM) task improves performance and reduces blood flow in the right anterior middle/superior frontal cortex, an area known to be important for WM. The purpose of this study was to evaluate the interaction between WM task demands and cholinergic enhancement on neural responses in the prefrontal cortex. Regional cerebral blood flow (rCBF) was measured using H(2)(15)O and positron emission tomography, as 10 young healthy volunteers performed a parametrically varied match-to-sample WM for faces task. For each item, a picture of a face was presented, followed by a delay (1, 6, 11, or 16 sec), then by the presentation of two faces. For control items, nonsense pictures were presented in the same spatial and temporal manner. All conditions were performed during an intravenous infusion of saline and physostigmine (1 mg/hr). Subjects were blind to the substance being infused. Reaction time increased significantly with WM delay, and physostigmine decreased reaction time across delay conditions. Significant task-related rCBF increases during saline infusion were seen in superior frontal, middle frontal, and inferior frontal regions, and the response magnitudes in the regions increased systematically with task difficulty. In all of these prefrontal regions, physostigmine administration significantly reduced rCBF during task, particularly at longer task delays, so that no correlation between task delay and rCBF was observed. In the ventral visual cortex, physostigmine increased rCBF at longer task delays in medial regions, and decreased rCBF over delay conditions in lateral cortical areas. These results indicate that, during cholinergic potentiation, brain activity in prefrontal regions is not modulated by increases in WM task demands, and lends further support to the hypothesis that cholinergic modulation enhances visual processing, making the task easier to perform, and thus, compensate for the need to recruit prefrontal cortical regions as task demands increase.

Differential Lateralization for Words and Faces: Category or Psychophysics?

Evelyne Mercure — 2008-04-23T15:06:27-00:00

Journal of cognitive neuroscience (16 April 2008)

Abstract This set of three experiments assessed the influence of different psychophysical factors on the lateralization of the N170 event-related potential (ERP) component to words and faces. In all experiments, words elicited a left-lateralized N170, whereas faces elicited a right-lateralized or nonlateralized N170 depending on presentation conditions. Experiment 1 showed that lateralization for words (but not for faces) was influenced by spatial frequency. Experiment 2 showed that stimulus presentation time influenced N170 lateralization independently of spatial frequency composition. Finally, Experiment 3 showed that stimulus size and resolution did not influence N170 lateralization, but did influence N170 amplitude, albeit differentially for words and faces. These findings suggest that differential lateralization for words and faces, at least as measured by the N170, is influenced by spatial frequency (words), stimulus presentation time, and category.

Prestimulus Cortical Activity is Correlated with Speed of Visuomotor Processing.

Yan Zhang — 2008-04-10T14:36:58-00:00

Journal of cognitive neuroscience (27 March 2008)

Abstract Response time (RT) is an important behavioral measure of the overall efficacy of sensorimotor processing and is known to vary significantly from trial to trial. Past work on how stimulus evoked cortical responses contribute to RT variability has helped delineate the stages of neuronal information processing. Much less is known about how the state of the brain immediately preceding the stimulus onset (prestimulus) affects RT. We addressed this problem by analyzing data from three macaque monkeys trained to perform a visuomotor pattern discrimination task. Local field potentials were recorded from up to 16 bipolar surface-to-depth electrodes widely distributed over one cerebral hemisphere in each monkey. The degree of linear correlation between RT and prestimulus spectral power was determined over a wide range of frequencies. In the prefrontal cortex, prestimulus power in the beta range (14-30 Hz) was negatively correlated with RT in two monkeys, suggesting a possible role of activity in this frequency range in the mediation of top-down control of visuomotor processing. In the sensorimotor cortex, prestimulus power in the beta range was positively correlated with RT in two monkeys, consistent with the hypothesis that oscillations in this range support the maintenance of steady-state motor output. In visual occipital and temporal lobe areas, prestimulus power in the alpha/low beta range (8-20 Hz) showed positive correlations with RT in three monkeys, possibly reflecting a spatially specific disengagement of visual anticipatory attention. Through measurement of prestimulus spectral coherence, it was further determined that sites showing similar patterns of correlation between spectral power and RT were also linked together in synchronized networks.

Sparse but not `Grandmother-cell' coding in the medial temporal lobe

Quian Quiroga — 2008-02-14T12:17:10-00:00

Trends in Cognitive Sciences, Vol. In Press, Corrected Proof

Although a large number of neuropsychological and imaging studies have demonstrated that the medial temporal lobe (MTL) plays an important role in human memory, there are few data regarding the activity of neurons involved in this process. The MTL receives massive inputs from visual cortical areas, and evidence over the last decade has consistently shown that MTL neurons respond selectively to complex visual stimuli. Here, we focus on how the activity patterns of these cells might reflect the transformation of visual percepts into long-term memories. Given the very sparse and abstract representation of visual information by these neurons, they could in principle be considered as `grandmother cells'. However, we give several arguments that make such an extreme interpretation unlikely.