Object-selective Areas Research Articles

Gestalts at threshold could reveal Gestalts as predictions

We review and revisit the predictive processing inspired “Gestalts as predictions” hypothesis. The study of Gestalt phenomena at and below threshold can help clarify the role of higher-order object selective areas and feedback connections in mid-level vision. In two psychophysical experiments assessing manipulations of contrast and configurality we showed that: (1) Gestalt phenomena are robust against saliency manipulations across the psychometric function even below threshold (with the accuracy gains and higher saliency associated with Gestalts being present even around chance performance); and (2) peak differences between Gestalt and control conditions happened around the time where responses to Gestalts are starting to saturate (mimicking the differential contrast response profile of striate vs. extra-striate visual neurons). In addition, Gestalts are associated with steeper psychometric functions in all experiments. We propose that these results reflect the differential engagement of object-selective areas in Gestalt phenomena and of information- or percept-based processing, as opposed to energy- or stimulus-based processing, more generally. In addition, the presence of nonlinearities in the psychometric functions suggest differential top-down modulation of the early visual cortex. We treat this as a proof of principle study, illustrating that classic psychophysics can help assess possible involvement of hierarchical predictive processing in Gestalt phenomena.

Signposts in the Fog: Objects Facilitate Scene Representations in Left Scene-selective Cortex.

We internally represent the structure of our surroundings even when there is little layout information available in the visual image, such as when walking through fog or darkness. One way in which we disambiguate such scenes is through object cues; for example, seeing a boat supports the inference that the foggy scene is a lake. Recent studies have investigated the neural mechanisms by which object and scene processing interact to support object perception. The current study examines the reverse interaction by which objects facilitate the neural representation of scene layout. Photographs of indoor (closed) and outdoor (open) real-world scenes were blurred such that they were difficult to categorize on their own but easily disambiguated by the inclusion of an object. fMRI decoding was used to measure scene representations in scene-selective parahippocampal place area (PPA) and occipital place area (OPA). Classifiers were trained to distinguish response patterns to fully visible indoor and outdoor scenes, presented in an independent experiment. Testing these classifiers on blurred scenes revealed a strong improvement in classification in left PPA and OPA when objects were present, despite the reduced low-level visual feature overlap with the training set in this condition. These findings were specific to left PPA/OPA, with no evidence for object-driven facilitation in right PPA/OPA, object-selective areas, and early visual cortex. These findings demonstrate separate roles for left and right scene-selective cortex in scene representation, whereby left PPA/OPA represents inferred scene layout, influenced by contextual object cues, and right PPA/OPA represents a scene's visual features.

Functional modulation of contralateral bias in early and object-selective areas after stroke of the occipital ventral cortices

Object agnosia is a rare symptom, occurring mainly after bilateral damage of the ventral visual cortex. Most patients suffering from unilateral ventral lesions are clinically non-agnosic. Here, we studied the effect of unilateral occipito-temporal lesions on object categorization and its underlying neural correlates in visual areas. Thirteen non-agnosic stroke patients and twelve control subjects performed an event-related rapid object categorization task in the fMRI scanner where images were presented either to the left or to the right of a fixed point. Eight patients had intact central visual fields within at least 10° eccentricity while five patients showed an incomplete hemianopia. Patients made more errors than controls for both contra- and ipsilesional presentation, meaning that object categorization was impaired bilaterally in both patient groups. The activity in cortical visual areas is usually higher when a stimulus is presented contralaterally compared to presented ipsilaterally (contralateral bias). A region of interest analysis of early visual (V1–V4) and object-selective areas (lateral occipital complex, LOC; fusiform face area, FFA; and parahippocampal place area, PPA) revealed that the lesioned-hemisphere of patients showed reduced contralateral bias in early visual areas and LOC. In contrast, literally no contralateral bias in FFA and PPA was found. These findings indicate disturbed processing in the lesioned hemisphere, which might be related to the processing of visually presented objects. Thus, unilateral occipito-temporal damage leads to altered contralateral bias in the lesioned hemisphere, which might be the cause of impaired categorization performance in both visual hemifields in clinically non-agnosic patients. We conclude that both hemispheres need to be functionally intact for unimpaired object processing.

Typicality sharpens category representations in object-selective cortex

The purpose of categorization is to identify generalizable classes of objects whose members can be treated equivalently. Within a category, however, some exemplars are more representative of that concept than others. Despite long-standing behavioral effects, little is known about how typicality influences the neural representation of real-world objects from the same category. Using fMRI, we showed participants 64 subordinate object categories (exemplars) grouped into 8 basic categories. Typicality for each exemplar was assessed behaviorally and we used several multi-voxel pattern analyses to characterize how typicality affects the pattern of responses elicited in early visual and object-selective areas: V1, V2, V3v, hV4, LOC. We found that in LOC, but not in early areas, typical exemplars elicited activity more similar to the central category tendency and created sharper category boundaries than less typical exemplars, suggesting that typicality enhances within-category similarity and between-category dissimilarity. Additionally, we uncovered a brain region (cIPL) where category boundaries favor less typical categories. Our results suggest that typicality may constitute a previously unexplored principle of organization for intra-category neural structure and, furthermore, that this representation is not directly reflected in image features describing natural input, but rather built by the visual system at an intermediate processing stage.

When does repetition suppression depend on repetition probability?

When does repetition suppression depend on repetition probability?

Functional modulation of object-selective areas in stroke patients with ventral cortical lesions

Functional modulation of object-selective areas in stroke patients with ventral cortical lesions

Do object-category selective regions in the ventral visual stream represent perceived distance information?

It is well established that scenes and objects elicit a highly selective response in specific brain regions in the ventral visual cortex. An inherent difference between these categories that has not been explored yet is their perceived distance from the observer (i.e. scenes are distal whereas objects are proximal). The current study aimed to test the extent to which scene and object selective areas are sensitive to perceived distance information independently from their category-selectivity and retinotopic location. We conducted two studies that used a distance illusion (i.e., the Ponzo lines) and showed that scene regions (the parahippocampal place area, PPA, and transverse occipital sulcus, TOS) are biased toward perceived distal stimuli, whereas the lateral occipital (LO) object region is biased toward perceived proximal stimuli. These results suggest that the ventral visual cortex plays a role in representing distance information, extending recent findings on the sensitivity of these regions to location information. More broadly, our findings imply that distance information is inherent to object recognition.

Functional modulation of object-selective areas in stoke patients with ventral cortical lesions

Functional modulation of object-selective areas in stoke patients with ventral cortical lesions

Stimulation of Category-Selective Brain Areas Modulates ERP to Their Preferred Categories

Neural selectivity to specific object categories has been demonstrated in extrastriate cortex with both functional MRI [1-3] and event-related potential (ERP) [4, 5]. Here we tested for a causal relationship between the activation of category-selective areas and ERP to their preferred categories. Electroencephalogram (EEG) was recorded while participants observed faces and headless bodies. Concurrently with EEG recording, we delivered two pulses of transcranial magnetic stimulation (TMS) over the right occipital face area (OFA) or extrastriate body area (EBA) at 60 and 100 ms after stimulus onset. Results showed a clear dissociation between the stimulated site and the stimulus category on ERP modulation: stimulation of the OFA significantly increased the N1 amplitude to faces but not to bodies, whereas stimulation of the EBA significantly increased the N1 amplitude to bodies but not to faces. These findings provide the first evidence for a specific and causal link between activity in category-selective networks and scalp-recorded ERP to their preferred categories. This result also demonstrates that the face and body N1 reflects several nonoverlapping neural sources, rather than changes in face-selective mechanisms alone. Lastly, because early stimulation (60-100 ms) affected selectivity of a later ERP component (150-200 ms), the results could imply a feed-forward connection between occipital and temporal category-selective areas.

Decoding object-based attention signals in the human brain

Visual attention can be directed to spatial locations and various features, as well as to a unitary object independently of spatial and feature variations. Previous work has shown object-based attention can modulate neural activity in category-selective areas in the ventral visual cortex. However, whether earlier visual areas can be modulated by object-based attention and how higher-order areas control and represent the deployment of object-based attention is not clear. To investigate the neural mechanism of object-based attention, we presented two superimposed objects with similar shape that occupied the same spatial location, and asked participants to perform an attention-demanding task on one of the objects. We observed enhanced fMRI response for object-attended condition compared to a neutral condition in a network of occipital-parietal-frontal areas. There was no difference in overall sustained fMRI response between attending to different objects in any attention task regions. Using multivariate pattern analysis (MVPA), however, we successfully “read out” the attended object from activity patterns in both early visual areas (V1 to MT+), object-selective areas (lateral occipital complex, LOC), and some parietal and frontal areas (e.g., IPS, MFG, and SFG). These results indicate that neural activity in multiple visual areas can be modulated by object-based attention. Furthermore, parietal and frontal cortical regions contain neural signals related to priority of attended object.

Orthogonal representations of object category and location in object selective cortex

Theories of object recognition often call upon the notion of invariance to account for our ability to recognize objects across many naturally occurring transformations (e.g. size and viewpoint), including changes in spatial position. To investigate this, we measured brain activity using fMRI while subjects viewed four categories of objects (faces, houses, animals, and cars) displayed to four locations in the visual field. In our analysis, we first used principal component analysis to decompose the responses of object selective areas into a set of orthogonal component activation patterns. These components were used by a linear classifier to decode the category of the object displayed to the observer. The results of the classification analysis showed that object selective areas robustly code the position of objects. We further investigated how the brain supports our ability to recognize objects across different locations. In an examination of the individual components, we found subsets that retain the ability to extract object category information across different locations. These components, which are orthogonal to components that rely on position, could be utilized to solve the problem of invariance. Notably, this represents a population response solution, which is consistent with recent modeling efforts. The orthogonality of these representations is exemplified in our analysis of FFA and PPA. In terms of the components that specified object category, the specialization of these areas was clear. The preferred category had more object category components; these components also accounted for a large proportion of the object related activity in these areas. In contrast, the representation of space in these areas was found to be roughly equivalent for the preferred and non-preferred object categories.

The representation of diagnostic chromatic texture in object-selective areas of human visual cortex [abstract

The representation of diagnostic chromatic texture in object-selective areas of human visual cortex [abstract

FMRI–Adaptation Studies of Viewpoint Tuning in the Extrastriate and Fusiform Body Areas

People are easily able to perceive the human body across different viewpoints, but the neural mechanisms underpinning this ability are currently unclear. In three experiments, we used functional MRI (fMRI) adaptation to study the view-invariance of representations in two cortical regions that have previously been shown to be sensitive to visual depictions of the human body--the extrastriate and fusiform body areas (EBA and FBA). The BOLD response to sequentially presented pairs of bodies was treated as an index of view invariance. Specifically, we compared trials in which the bodies in each image held identical poses (seen from different views) to trials containing different poses. EBA and FBA adapted to identical views of the same pose, and both showed a progressive rebound from adaptation as a function of the angular difference between views, up to approximately 30 degrees. However, these adaptation effects were eliminated when the body stimuli were followed by a pattern mask. Delaying the mask onset increased the response (but not the adaptation effect) in EBA, leaving FBA unaffected. We interpret these masking effects as evidence that view-dependent fMRI adaptation is driven by later waves of neuronal responses in the regions of interest. Finally, in a whole brain analysis, we identified an anterior region of the left inferior temporal sulcus (l-aITS) that responded linearly to stimulus rotation, but showed no selectivity for bodies. Our results show that body-selective cortical areas exhibit a similar degree of view-invariance as other object selective areas--such as the lateral occipitotemporal area (LO) and posterior fusiform gyrus (pFs).

Retinotopically Specific Reorganization of Visual Cortex for Tactile Pattern Recognition

Although previous studies have shown that Braille reading and other tactile discrimination tasks activate the visual cortex of blind and sighted people, it is not known whether this kind of crossmodal reorganization is influenced by retinotopic organization. We have addressed this question by studying "S," a visually impaired adult with the rare ability to read print visually and Braille by touch. S had normal visual development until 6 years of age, and thereafter severe acuity reduction due to corneal opacification, but no evidence of visual-field loss. Functional magnetic resonance imaging revealed that, in S's early visual areas, tactile information processing activated what would be the foveal representation for normally sighted individuals, and visual information processing activated what would be the peripheral representation. Control experiments showed that this activation pattern was not due to visual imagery. S's high-level visual areas, which correspond to shape- and object-selective areas in normally sighted individuals, were activated by both visual and tactile stimuli. The retinotopically specific reorganization in early visual areas suggests an efficient redistribution of neural resources in the visual cortex.

Temporal Limitations in Object Processing Across the Human Ventral Visual Pathway

Behavioral studies have shown that object recognition becomes severely impaired at fast presentation rates, indicating a limitation in temporal processing capacity. Here, we studied whether this behavioral limit in object recognition reflects limitations in the temporal processing capacity of early visual areas tuned to basic features or high-level areas tuned to complex objects. We used functional MRI (fMRI) to measure the temporal processing capacity of multiple areas along the ventral visual pathway progressing from the primary visual cortex (V1) to high-level object-selective regions, specifically the fusiform face area (FFA) and parahippocampal place area (PPA). Subjects viewed successive images of faces or houses at presentation rates varying from 2.3 to 37.5 items/s while performing an object discrimination task. Measures of the temporal frequency response profile of each visual area revealed a systematic decline in peak tuning across the visual hierarchy. Areas V1-V3 showed peak activity at rapid presentation rates of 18-25 items/s, area V4v peaked at intermediate rates (9 items/s), and the FFA and PPA peaked at the slowest temporal rates (4-5 items/s). Our results reveal a progressive loss in the temporal processing capacity of the human visual system as information is transferred from early visual areas to higher areas. These data suggest that temporal limitations in object recognition likely result from the limited processing capacity of high-level object-selective areas rather than that of earlier stages of visual processing.

Neural basis of redundancy effects in visual object categorization

Bilateral redundant information often leads to improved detection performance compared to only unilateral input. This experiment investigates redundancy effects at the level of object processing in behavioral and functional imaging data. Subjects received different combinations of categorical information presented to both visual hemifields simultaneously. For pictures of faces as well as for pictures of buildings, response latencies were faster when two pictures from the same object category were presented compared to two pictures from different categories. This behavioral advantage was accompanied by increased activation in the respective object-selective areas, i.e. in the Fusiform Face Area (FFA) for pictures of faces and in the Parahippocampal Place Areas (PPAs) for pictures of buildings. These results suggest an involvement of visual object-selective areas in the behavioral redundancy gain.

Increased Neural Efficiency with Repeated Performance of a Working Memory Task is Information-type Dependent

Unlike tasks in which practice leads to an automatic stimulus-response association, it is thought working memory (WM) tasks continue to require cognitive control processes after repeated performance. Previous studies investigating WM task repetition are in accord with this. However, it is unclear whether changes in neural activity after repetition imply alterations in general control processes common to all WM tasks or are specific to the selection, encoding and maintenance of the relevant information. In the present study, functional magnetic resonance imaging (fMRI) was used to examine changes during sample, delay and test periods during repetition of both object and spatial delayed recognition tasks. We found decreases in fMRI activation in both spatial and object-selective areas after spatial WM task repetition, independent of behavioral performance. Few areas showed changed activity after object WM task repetition. These results indicate that spatial task repetition leads to increased efficiency of maintaining task-relevant information and improved ability to filter out task-irrelevant information. The specificity of this repetition effect to the spatial task suggests a difference exists in the nature of the representation of object and spatial information and that their maintenance in WM is likely subserved by different neural systems.

Differential activation of object-selective visual areas by passive viewing of pictures and words

Functional imaging has shown that pictures of faces (N. Kanwisher, J. McDermott, M.M. Chun, The fusiform face area: a module in human extrastriate cortex specialized for face perception, J. Neurosci. 17 (1997) 4302–4311) and buildings (R. Epstein, N. Kanwisher, A cortical representation of the local visual environment, Nature 391 (1998) 598–601) activate different regions within the lateral occipital complex (LOC). To investigate effects of stimulus format on activation in these areas, we used event-related fMRI to measure brain activity during the passive viewing of pictures showing buildings and faces, and of words identifying these pictures. Consistent with earlier findings, pictures of faces activated bilateral regions in the lateral fusiform gyri, whereas pictures of buildings activated bilateral regions in the parahippocampal gyri. Analyzing the activation elicited by visually presenting the written names of the pictures, however, we did not find an effect of word meaning on the fMRI signal change in these areas: fMRI signal changes for the names of faces and the names of buildings did not differ in any of the areas selectively activated by the corresponding pictures. In general, both word conditions and non-preferred picture conditions elicited similar signal amplitudes. While presentation of words did not lead to strong activation in object-specific areas, activation for words of both categories was found in the left occipito-temporal cortex, close to the location which has tentatively been called ‘visual word form area’ (L. Cohen, S. Dehaene, L. Naccache, S. Lehéricy, G. Dehaene-Lambertz, et al., The visual word form are: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients, Brain 123 (2000) 291–307), revealing that words were processed effectively during the experiment. Taken together, these results show that names of pictures do not automatically activate the corresponding object-selective areas.

Neural responses to Mooney images reveal a modular representation of faces in human visual cortex

The way in which information about objects is represented in visual cortex remains controversial. One model of human object recognition poses that information is processed in modules, highly specialised for different categories of objects; an opposing model appeals to a distributed representation across a large network of visual areas. We addressed this debate by monitoring activity in face- and object-selective areas while human subjects viewed ambiguous face stimuli (Mooney faces). The measured neural response in the face-selective region of the fusiform gyrus was greater when subjects reported seeing a face than when they perceived the image as a collection of blobs. In contrast, there was no difference in magnetic resonance response between face and no-face perceived events in either the face-selective voxels of the superior temporal sulcus or the object-selective voxels of the parahippocampal gyrus and lateral occipital complex. These results challenge the concept that neural representation of faces is distributed and overlapping and suggest that the fusiform gyrus is tightly linked to the awareness of faces.