The physiological blind spot corresponds to the optic disc where the retina contains no light-detecting photoreceptor cells. Our perception seemingly fills in this gap in input. Here we suggest that rather than an active process, such perceptual filling-in could instead be a consequence of the integration of visual inputs at higher stages of processing discounting the local absence of retinal input. Using functional brain imaging, we resolved the retinotopic representation of the physiological blind spot in early human visual cortex and (...) measured responses while participants perceived filling-in. Responses in early visual areas simply reflected the absence of visual input. In contrast, higher extrastriate regions responded more to stimuli in the eye containing the blind spot than the fellow eye. However, this signature was independent of filling-in. We argue that these findings agree with philosophical accounts that posit that the concept of filling-in of absent retinal input is unnecessary. (shrink)

activity” has been considered to play a major role in the short-term maintenance of memories. Many studies since then have provided support for this view and greatly advanced our knowledge of the effects of stimulus type and modality on delay activity and its temporal dynamics. In humans, working memory has also been a subject of intense investigation using scalp and intracranial electroencephalography as well as magnetoencephalography, which provide estimates of local population activity. The published findings include reports of systematic changes (...) in signal amplitude during working memory in the theta, alpha, beta. (shrink)

The neural mechanisms underlying behavioral improvement in the detection or discrimination of visual stimuli following learning are still ill understood. Studies in nonhuman primates have shown relatively small and, across studies, variable effects of fine discrimination learning in primary visual cortex when tested outside the context of the learned task. At later stages, such as extrastriate area V4, extensive practice in fine discrimination produces more consistent effects upon responses and neural tuning. In V1 and V4, the effects of learning (...) were most prominent in those neurons that can contribute the most reliable information about the trained stimuli. I suggest that, depending on the particulars of the task demands, neurons at various stages of stimulus and task processing can change their tuning and responses, so that execution of the task will produce a higher frequency of reward. I speculate that the sort of changes that will occur depend on the task and on stimulus analysis require- ments, and they may vary from changes in bottom-up stimulus processing ⁄ tuning within early visual areas or more efficient readout of early visual areas to top-down driven changes in response proper- ties of these areas. (shrink)

Face perception, perhaps the most highly developed visual skill in humans, is mediated by a distributed neural system in humans that is comprised of multiple, bilateral regions. We propose a model for the organization of this system that emphasizes a distinction between the representation of invariant and changeable aspects of faces. The representation of invariant aspects of faces underlies the recognition of individuals, whereas the representation of changeable aspects of faces, such as eye gaze, expression, and lip movement, underlies the (...) perception of information that facilitates social communication. The model is also hierarchical insofar as it is divided into a core system and an extended system. The core system is comprised of occipitotemporal regions in extrastriate visual cortex that mediate the visual analysis of faces. In the core system, the representation of invariant aspects is mediated more by the face-responsive region in the fusiform gyrus, whereas the representation of changeable aspects is mediated more by the face-responsive region in the superior temporal sulcus. The extended system is comprised of regions from neural systems for other cognitive functions that can be recruited to act in concert with the regions in the core system to extract meaning from faces. (shrink)

We present a theory of human artistic experience and the neural mechanisms that mediate it. Any theory of art has to ideally have three components. The logic of art: whether there are universal rules or principles; The evolutionary rationale: why did these rules evolve and why do they have the form that they do; What is the brain circuitry involved? Our paper begins with a quest for artistic universals and proposes a list of ‘Eight laws of artistic experience’ -- a (...) set of heuristics that artists either consciously or unconsciously deploy to optimally titillate the visual areas of the brain. One of these principles is a psychological phenomenon called the peak shift effect: If a rat is rewarded for discriminating a rectangle from a square, it will respond even more vigorously to a rectangle that is longer and skinnier that the prototype. We suggest that this principle explains not only caricatures, but many other aspects of art. Example: An evocative sketch of a female nude may be one which selectively accentuates those feminine form-attributes that allow one to discriminate it from a male figure; a Boucher, a Van Gogh, or a Monet may be a caricature in ‘colour space’ rather than form space. Even abstract art may employ ‘supernormal’ stimuli to excite form areas in the brain more strongly than natural stimuli. Second, we suggest that grouping is a very basic principle. The different extrastriate visual areas may have evolved specifically to extract correlations in different domains , and discovering and linking multiple features into unitary clusters -- objects -- is facilitated and reinforced by direct connections from these areas to limbic structures. In general, when object-like entities are partially discerned at any stage in the visual hierarchy, messages are sent back to earlier stages to alert them to certain locations or features in order to look for additional evidence for the object . Finally, given constraints on allocation of attentional resources, art is most appealing if it produces heightened activity in a single dimension rather than redundant activation of multiple modules. This idea may help explain the effectiveness of outline drawings and sketches, the savant syndrome in autists, and the sudden emergence of artistic talent in fronto-temporal dementia. In addition to these three basic principles we propose five others, constituting a total of ‘eight laws of aesthetic experience’. (shrink)

Blindsight, the ability to blindly discriminate wavelength and other aspects of stimuli in a blind field, sometimes occurs in people with lesions to striate (V1) cortex. There is currently no consensus on whether qualitative color information of the sort that is normally computed by double opponent cells in striate cortex is indeed computed in blindsight but doesn’t reach awareness, perhaps owing to abnormal neuron responsiveness in striate or extra-striate cortical areas, or is not computed at all. The existence of primesight, (...) the experience of colored afterimages in blindsight, has been taken to suggest that qualitative color information is computed either in pre-striate or striate cortical areas but is not broadcast to working memory. I argue here that a recent study in which color phosphenes were induced in a blindsighter using bilateral transcranial magnetic stimulation indicates that computations necessary for conscious color vision are lost in blindsight. Owing to this loss, the neural responsiveness in extrastriate cortical areas is abnormal and hence is unable to give rise to color awareness. Blindsight is thus degraded vision in which the computations necessary for conscious color vision have been lost. (shrink)

Action semantics enables us to plan actions with objects and to predict others' object-directed actions as well. Previous studies have suggested that action semantics are represented in a fronto-parietal action network that has also been implicated to play a role in action observation. In the present fMRI study it was investigated how activity within this network changes as a function of the predictability of an action involving multiple objects and requiring the use of action semantics. Participants performed an action prediction (...) task in which they were required to anticipate the use of a centrally presented object that could be moved to an associated target object (e.g., hammer—nail). The availability of actor information (i.e., presenting a hand grasping the central object) and the number of possible target objects (i.e., 0, 1, or 2 target objects) were independently manipulated, resulting in different levels of predictability. It was found that making an action prediction based on actor information resulted in an increased activation in the extrastriate body area (EBA) and the fronto-parietal action observation network (AON). Predicting actions involving a target object resulted in increased activation in the bilateral IPL and frontal motor areas. Within the AON, activity in the left inferior parietal lobe (IPL) and the left premotor cortex (PMC) increased as a function of the level of action predictability. Together these findings suggest that the left IPL represents stored hand-postures that can be used for planning object-directed actions and for predicting other's actions as well. (shrink)

Creating focal lesions in primary visual cortex (V1) provides an opportunity to study the role of extra-geniculo-striate pathways for activating extrastriate visual cortex. Previous studies have shown that more than 95% of neurons in macaque area V2 and V3 stop firing after reversibly cooling V1 [1,2,3]. However, no studies on long term recovery in areas V2, V3 following permanent V1 lesions have been reported in the macaque. Here we use macaque fMRI to study area V2, V3 activity patterns from (...) 1 to 22 months after lesioning area V1. We find that visually driven BOLD responses persist inside the V1-lesion projection zones (LPZ) of areas V2 and V3, but are reduced in strength by ,70%, on average, compared to prelesion levels. Monitoring the LPZ activity over time starting one month following the V1 lesion did not reveal systematic changes in BOLD signal amplitude. Surprisingly, the retinotopic organization inside the LPZ of areas V2, V3 remained similar to that of the non-lesioned hemisphere, suggesting that LPZ activation in V2, V3 is not the result of input arising from nearby (non-lesioned) V1 cortex. Electrophysiology recordings of multi-unit activity corroborated the BOLD observations: visually driven multi-unit responses could be elicited inside the V2 LPZ, even when the visual stimulus was entirely contained within the scotoma induced by the V1 lesion. Restricting the stimulus to the intact visual hemi-field produced no significant BOLD modulation inside the V2, V3 LPZs. We conclude that the observed activity patterns are largely mediated by parallel, V1-bypassing, subcortical pathways that can activate areas V2 and V3 in the absence of V1 input. Such pathways may contribute to the behavioral phenomenon of blindsight. (shrink)

A key question in understanding visual awareness is whether any single cortical area is indispensable. In a transcranial magnetic stimulation experiment, we show that observers' awareness of activity in extrastriate area VS depends on the amount of activity in striate cortex (Vl). From the timing and pattern of effects, we infer that back-projections from extrastriate cortex influence information content in Vl, but it is Vl that determines whether that information reaches awareness.

Optic neuropathies are conditions that cause disease to the optic nerve, and can result in loss of visual acuity and/or visual field defects. An improved understanding of how these conditions affect the entire visual system is warranted, to better predict and/or restore the visual loss. In this article, we review visually-driven functional magnetic resonance imaging (fMRI) studies of optic neuropathies, including glaucoma and optic neuritis (ON); we also discuss traumatic optic neuropathy (TON). Optic neuropathy-related vision loss results in fMRI deficit (...) within the visual cortex, and is often strongly correlated with clinical severity measures. Using predominantly flickering checkerboard stimuli, glaucoma studies indicated retinotopic-specific cortical alteration with more prominent deficits in advanced than in early glaucoma. Some glaucoma studies indicate a reorganized visual cortex. ON studies have indicated that the impacted cortical areas are briefly hyperactive. For ON, brain deficits are greater in the acute stages of the disease, followed by (near) normalization of responses of the LGN, visual cortex, and the dorsal visual stream, but not the ventral extrastriate cortex. Visually-driven fMRI is sensitive, at least in ON, in discriminating patients from controls, as well as the affected eye from the fellow eye within patients. The use of a greater variety of stimuli beyond checkerboards (e.g., visual motion and object recognition) in recent ON studies is encouraging, and needs to continue to disentangle the results in terms of change over time. Finally, visually-driven fMRI has not yet been applied in TON, although preliminary efforts suggest it may be feasible. Future fMRI studies of optic neuropathies should consider using more complex visual stimuli, and inter-regional analysis methods including functional connectivity. We suggest that a more systematic longitudinal comparison of optic neuropathies with advanced fMRI would provide improved diagnostic and prognostic information. (shrink)

Three of the most robust functional landmarks in the human brain are the selective responses to faces in the fusiform face area (FFA), scenes in the parahippocampal place area (PPA), and bodies in the extrastriate body area (EBA). Are the selective responses of these regions present early in development or do they require many years to develop? Prior evidence leaves this question unresolved. We designed a new 32-channel infant magnetic resonance imaging (MRI) coil and collected high-quality functional MRI (fMRI) (...) data from infants (2–9 months of age) while they viewed stimuli from four conditions—faces, bodies, objects, and scenes. We find that infants have face-, scene-, and body-selective responses in the location of the adult FFA, PPA, and EBA, respectively, powerfully constraining accounts of cortical development. (shrink)

A review of the patterns of brain activation observed in implicit and explicit memory tasks indicates that during conscious retrieval studied items are first retrieved nonconsciously and are retained in a buffer at the extrastriate cortex. It also indicates that the awareness of the retrieved item is made possible by the activation of a reentrant signaling loop between the extrastriate and left prefrontal cortices.

In order to study whether there exist a period of activity in the human early visual cortex that contributes exclusively to visual awareness, we applied transcranial magnetic stimulation over the early visual cortex and measured subjective visual awareness during visual forced-choice symbol or orientation discrimination tasks. TMS produced one dip in awareness 60–120 ms after stimulus onset, while forced-choice orientation discrimination was suppressed between 60 and 90 ms and symbol discrimination between 60 and 120 ms. Thus, a time window specific (...) to visual awareness was found only in the orientation condition at 120 ms. The results imply that both conscious and unconscious perception depend on activity in early visual areas. On the basis of previous estimates of neural processing speed, we suggest that the late part of the activity period most likely involve local extrastriate–striate interactions which provide the contents for visual awareness but are not themselves sufficient for awareness to arise. (shrink)

This volume explores how functional brain imaging techniques like positron emission tomography have influenced cognitive studies. The first chapter outlines efforts to relate human thought and cognition in terms of great books from the late 1800s through the present. Chapter 2 describes mental operations as they are measured in cognitive science studies. It develops a framework for relating mental operations to activity in nerve cells. In Chapter 3, the PET method is reviewed and studies are presented that use PET to (...) map the striate cortex and to activate extrastriate motion, color, and form areas. Chapter 4 shows how top down processes involving attention can lead to activation of these same areas in the detection of targets, visual search, and visual imagery. This chapter reveals complex networks of activations. Chapters 5 and 6 deal with the presentation of words. Chapter 5 illustrates PET studies of the anatomy of visual word processing and shows how the circuitry used for generating novel uses of words changes as the task becomes automated. Chapter 6 applies high density electrical recording to explore these activations in real time and to show how a constant anatomy can be reprogrammed by task instructions to produce and perform different cognitive tasks. Chapter 7 shows how studies of brain lesions and PET converge on common networks underlying attentional functions such as visual orienting, target detection, and maintenance of the alert state. Chapters 8 and 9 apply the network approach to examine normal development of attention in infants and pathological conditions resulting from brain damage, and psychiatric pathologies of depression, schizophrenia, and attention deficit disorder. In Chapter 10, new developments such as functional MRI are discussed in terms of future developments and integration of cognitive neuroscience. (shrink)

Background: We like to think about sexual activity as something fixed, basic and primal. However, this does not seem to fully capture reality. Even when we relish sex, we may be capable of mentalizing, talking, voluntarily postponing orgasm, and much more. This might indicate that the central control mechanisms of sexual activity are quite flexible and susceptible to learning mechanisms, and that cortical brain areas play a critical part. Objective: This study aimed to identify those cortical areas and mechanisms most (...) consistently implicated in sexual activity. Design: A comprehensive review of the human functional neuroimaging literature on sexual activity, i.e. genital stimulation and orgasm, is made. Results: Genital stimulation recruits the classical somatosensory matrix, but also areas far beyond that. The posterior insula may be particularly important for processing input from the engorged penis and coordinating penile responses. Extrastriate visual cortex tracks sexual arousal and responds to genital stimulation even when subjects have their eyes closed. The ventromedial prefrontal cortex is also tightly coupled to sexual arousal, but low activity in this area predicts high sexual arousal. Conclusion: This review has indicated cortical sites where activity is moderated by tactile genital inflow and high sexual arousal. Behavioral implications are discussed and where possible the relevance for learning mechanisms is indicated. Overall, it is clear that the cerebral cortex has something to say about sexual activity. Keywords: functional neuroimaging; insula; ventromedial prefrontal cortex; extrastriate visual cortex; penis; clitoris; orgasm (Published: 15 March 2012) Citation: Socioaffective Neuroscience & Psychology 2012, 2 : 17337 - DOI: 10.3402/snp.v2i0.17337. (shrink)

One problem of interpreting research on subconscious processing is the possibility that participants are weakly conscious of the stimuli. Here, we compared the fMRI BOLD response in healthy adults to clearly visible single letters with the response to letters presented in the absence of any behavioural evidence of visibility . No letter catch trials served as a control condition. Forced-choice responses did not differ from chance when letter-to-background contrast was low, whereas they were almost 100% correct when contrast was high. (...) A comparison of fMRI BOLD signals for supraliminal and subliminal letters with the control trials revealed a signal increase in left BA 37 . Comparison of supraliminal with subliminal letters showed a significant increase in the right inferior frontal gyrus . Finally, a comparison of subliminal with supraliminal letters showed increases in the left middle temporal gyrus and the right extrastriate cortex. (shrink)

What is the relationship between a visual percept and the underlying neuronal activity in parts of the brain? This manifesto reviews the theoretical framework of Crick and Kochfor answering these questions based on the neuroanatomy and physiology of mammalian cortex and associated subcortical structures. This evidence suggests that primates are not directly aware of neural activity in primary visual cortex, although they may be aware of such activity in extrastriate cortical areas. Psychophysical evidence in humans supporting this hypothesis is (...) discussed. (shrink)

This report concerns the fragmented visual percepts in a woman, TR, following a right entorhinal–perirhinal infarct. In a previous report, Weddell [Weddell, R. A. . A visual disorder producing highly selective deletion of recurring letters. Cortex, 41, 471–485] linked TR’s highly selective tendency to delete recurrent letters with her fragmented percepts. The conflation of same-identity form elements was attributed to anterior extrastriate damage, which reduced the amount of information sustainable in fully resolved visual percepts, and the present experimental investigation (...) of her subjective account of segment formation and resolution completes the story. She said that complex objects and long words first appeared as blurred regions, which sometimes included form elements. It is argued that figure-centred attentional mechanisms subdivided this blurred region into up to 3–4 parts. String length, lexical status , and background colour and/or luminance determined fragment length. Two rules described the fragment resolution sequence: largest segments usually resolved first, left-to-right resolution accounting for a few sequences. This resolution sequence occurred when stimuli were exposed too briefly for saccadic exploration, implicating endogenous attentional shifts. Experiment 4 confirmed TR’s assertion that spatial, orthographic, and phonological information were stored during the fragment resolution process. Moreover, TR exerted considerable voluntarily control over the fragment resolution sequence and some influence over fragment length. Finally, these findings were interpreted in terms of an extended version of a neural network model of vision largely derived from nonhuman primate studies. (shrink)

Little is known about distance processing in patients with posterior brain damage. Although many investigators have claimed that distance estimates are normal or abnormal in some of these patients, many of these observations were made informally and the examiners often asked for relative, and not absolute, distance estimates. The present investigation served two purposes. First, we wanted to contrast the use of distance information in peripersonal space for perceptual report as opposed to visuomotor control in our visual form agnosic patient, (...) DF. Second, we wanted to see to what extent her abilities to process distance cues were dependent on binocular vision, in light of Milner et al.'s (1991) observations of preserved stereopsis in DF, and Dijkerman et al.'s (1996) and Marotta et al.'s (1997) observations that her visual guidance of grasping may be particularly dependent on binocular vision of the target. We hypothesized that DF's visuomotor responses would show normal sensitivity to target distance, while her perceptual estimates would not. In the first experiment, we required DF and two age- and sex-matched control subjects to reach out and grasp black cubes placed at varying distances, or to estimate the distance of the cubes from the hand starting position without making a reaching movement. In the second experiment, we required DF and two age-matched control subjects to point as rapidly and accurately as possible to small LED targets which differed in spatial location, under binocular and monocular conditions. The results showed that, relative to the control subjects, DF's grasping movements produced normal peak velocity-distance scaling-when she reached for blocks which varied in depth or pointed to LED targets which were presented at different distances in depth. In contrast, in the cube experiment, her verbal estimates of object distance were poorly scaled, although they improved slightly under the binocular conditions. The results are discussed in terms of current theories of processing streams in extrastriate visual cortex and the distinction between categorical and coordinate spatial processing. (shrink)

This paper presents a general computational treatment of how mammals are able to deal with visual objects and environments. The model tries to cover the entire range from behavior and phenomenological experience to detailed neural encodings in crude but computationally plausible reductive steps. The problems addressed include perceptual constancies, eye movements and the stable visual world, object descriptions, perceptual generalizations, and the representation of extrapersonal space.The entire development is based on an action-oriented notion of perception. The observer is assumed to (...) be continuously sampling the ambient light for information of current value. The central problem of vision is taken to be categorizing and locating objects in the environment. The critical step in this process is the linking of visual information to symbolic object descriptions; this is calledindexing, from the analogy of identifying a book from index terms. The system must also identifysituationsand use this knowledge to guide movement and other actions in the environment. The treatment focuses on the different representations of information used in the visual system.The four representational frames capture information in the following forms: retinotopic, head-based, symbolic, and allocentric. The functional roles of the four frames, the communication among them, and their suggested neurophysiological realization constitute the core of the paper. The model is perforce crude, but appears to be consistent with all relevant findings. (shrink)

Visual learning has been intensively studied in higher mammals, both during development and in adulthood. What is less clear is the extent and properties such plasticity may acquire following permanent damage to the adult visual system. Answering this question is important. Aside from improving our understanding of visual processing in the absence of an intact visual circuitry, such knowledge is essential for the development of effective therapies to rehabilitate the increasing number of people who suffer the functional consequences of damage (...) at different levels of their visual cortical hierarchy. This review summarizes the known characteristics of visual learning after adult visual cortex damage and begins to dissect some of the neural correlates of this process. (shrink)

Three experiments demonstrate that biological movement facilitates young infants’ recognition of the whole human form. A body discrimination task was used in which 6-, 9-, and 12-month-old infants were habituated to typical human bodies and then shown scrambled human bodies at the test. Recovery of interest to the scrambled bodies was observed in 9- and 12-month-old infants in Experiment 1, but only when the body images were animated to move in a biologically possible way. In Experiment 2, nonbiological movement was (...) incorporated into the typical and scrambled body images, but this did not facilitate body recognition in 9- and 12-month-olds. A preferential looking paradigm was used in Experiment 3 to determine if infants had a spontaneous preference for the scrambled versus typical body stimuli when these were both animated. The results showed that 12-month-olds preferred the scrambled body stimuli, 9-month-olds preferred the typical body stimuli and the 6-month-olds showed no preference for either type of body stimuli. These findings suggest that human body recognition involves integrating form and movement, possibly in the superior temporal sulcus, from as early as 9 months of life. (shrink)