The fusiform face area is not sufficient for face recognition: evidence from a patient with dense prosopagnosia and no occipital face area.

We tested functional activation for faces in patient D.F., who following acquired brain damage has a profound deficit in object recognition based on form (visual form agnosia) and also prosopagnosia that is undocumented to date. Functional imaging demonstrated that like our control observers, D.F. shows significantly more activation when passively viewing face compared to scene images in an area that is consistent with the fusiform face area (FFA) (p < 0.01). Control observers also show occipital face area (OFA) activation; however, whereas D.F.'s lesions appear to overlap the OFA bilaterally. We asked, given that D.F. shows FFA activation for faces, to what extent is she able to recognize faces? D.F. demonstrated a severe impairment in higher level face processing--she could not recognize face identity, gender or emotional expression. In contrast, she performed relatively normally on many face categorization tasks. D.F. can differentiate faces from non-faces given sufficient texture information and processing time, and she can do this is independent of color and illumination information. D.F. can use configural information for categorizing faces when they are presented in an upright but not a sideways orientation and given that she also cannot discriminate half-faces she may rely on a spatially symmetric feature arrangement. Faces appear to be a unique category, which she can classify even when she has no advance knowledge that she will be shown face images. Together, these imaging and behavioral data support the importance of the integrity of a complex network of regions for face identification, including more than just the FFA--in particular the OFA, a region believed to be associated with low-level processing.

Segregation and persistence of form in the lateral occipital complex.

While the lateral occipital complex (LOC) has been shown to be implicated in object recognition, it is unclear whether this brain area is responsive to low-level stimulus-driven features or high-level representational processes. We used scrambled shape-from-motion displays to disambiguate the presence of contours from figure-ground segregation and to measure the strength of the binding process for shapes without contours. We found persisting brain activation in the LOC for scrambled displays after the motion stopped indicating that this brain area subserves and maintains figure-ground segregation processes, a low-level function in the object processing hierarchy. In our second experiment, we found that the figure-ground segregation process has some form of spatial constancy indicating top-down influences. The persisting activation after the motion stops suggests an intermediate role in object recognition processes for this brain area and might provide further evidence for the idea that the lateral occipital complex subserves mnemonic functions mediating between iconic and short-term memory.

Behavioral and neuroimaging evidence for a contribution of color and texture information to scene classification in a patient with visual form agnosia.

A common notion is that object perception is a necessary precursor to scene perception. Behavioral evidence suggests, however, that scene perception can operate independently of object perception. Further, neuroimaging has revealed a specialized human cortical area for viewing scenes that is anatomically distinct from areas activated by viewing objects. Here we show that an individual with visual form agnosia, D.F., who has a profound deficit in object recognition but spared color and visual texture perception, could still classify scenes and that she was fastest when the scenes were presented in the appropriate color. When scenes were presented as black-and-white images, she made a large number of errors in classification. Functional magnetic resonance imaging revealed selective activation in the parahippocampal place area (PPA) when D.F. viewed scenes. Unlike control observers, D.F. demonstrated higher activation in the PPA for scenes presented in the appropriate color than for black-and-white versions. The results demonstrate that an individual with profound form vision deficits can still use visual texture and color to classify scenes-and that this intact ability is reflected in differential activation of the PPA with colored versions of scenes.

The effect of colour congruency on shape discriminations of novel objects.

Although visual object recognition is primarily shape driven, colour assists the recognition of some objects. It is unclear, however, just how colour information is coded with respect to shape in long-term memory and how the availability of colour in the visual image facilitates object recognition. We examined the role of colour in the recognition of novel, 3-D objects by manipulating the congruency of object colour across the study and test phases, using an old/new shape-identification task. In experiment 1, we found that participants were faster at correctly identifying old objects on the basis of shape information when these objects were presented in their original colour, rather than in a different colour. In experiments 2 and 3, we found that participants were faster at correctly identifying old objects on the basis of shape information when these objects were presented with their original part-colour conjunctions, rather than in different or in reversed part-colour conjunctions. In experiment 4, we found that participants were quite poor at the verbal recall of part-colour conjunctions for correctly identified old objects, presented as grey-scale images at test. In experiment 5, we found that participants were significantly slower at correctly identifying old objects when object colour was incongruent across study and test, than when background colour was incongruent across study and test. The results of these experiments suggest that both shape and colour information are stored as part of the long-term representation of these novel objects. Results are discussed in terms of how colour might be coded with respect to shape in stored object representations.

Naming and grasping common objects: a priming study.

This study examined the effects of priming on response latency when participants named and/or grasped common objects. A repetition-priming paradigm was used. An object was presented during a study phase and then was presented again during testing along with other objects that had not been seen before. In experiment 1, the studied objects were either named twice or grasped twice, named first and then grasped, or grasped first and then named. We found a strong priming effect (i.e., decreased latency) when naming was preceded by naming, as well as by grasping, but no priming effect when grasping was preceded by either naming or grasping. In experiment 2, we investigated the effects of priming in naming-naming and grasping-grasping paradigms, with and without a change in object orientation from study to test. As expected, we found significant priming of naming by naming, and the effect was not reduced by orientation change. Again, we found no evidence of priming in grasping. Experiment 3 was designed to examine how different kinds of perceptual and visuomotor processing (naming, orientation matching, orientation discrimination, simple observation, and grasping) during the study phase affect naming at a later test phase. We found significant priming of naming following all study conditions. Notably, the effect differed depending on how much "perceptual" processing was involved in the study phase. The results clearly indicate that perceptual/semantic processing is more dependent on memory than visuomotor processing, which instead relies more on moment-to-moment computations.

Ventral occipital lesions impair object recognition but not object-directed grasping: an fMRI study.

D.F., a patient with severe visual form agnosia, has been the subject of extensive research during the past decade. The fact that she could process visual input accurately for the purposes of guiding action despite being unable to perform visual discriminations on the same visual input inspired a novel interpretation of the functions of the two main cortical visual pathways or 'streams'. Within this theoretical context, the authors proposed that D.F. had suffered severe bilateral damage to her occipitotemporal visual system (the 'ventral stream'), while retaining the use of her occipitoparietal visual system (the 'dorsal stream'). The present paper reports a direct test of this idea, which was initially derived from purely behavioural data, before the advent of modern functional neuroimaging. We used functional MRI to examine activation in her ventral and dorsal streams during object recognition and object-directed grasping tasks. We found that D.F. showed no difference in activation when presented with line drawings of common objects compared with scrambled line drawings in the lateral occipital cortex (LO) of the ventral stream, an area that responded differentially to these stimuli in healthy individuals. Moreover, high-resolution anatomical MRI showed that her lesion corresponded bilaterally with the location of LO in healthy participants. The lack of activation with line drawings in D.F. mirrors her poor performance in identifying the objects depicted in the drawings. With coloured and greyscale pictures, stimuli that she can identify more often, D.F. did show some ventral-stream activation. These activations were, however, more widely distributed than those seen in control participants and did not include LO. In contrast to the absent or abnormal activation observed during these perceptual tasks, D.F. showed robust activation in the expected dorsal stream regions during object grasping, despite considerable atrophy in some regions of the parietal lobes. In particular, an area in the anterior intraparietal sulcus was activated more for grasping an object than for just reaching to that object, for both D.F. and controls. In conclusion, we have been able to confirm directly that D.F.'s visual form agnosia is associated with extensive damage to the ventral stream, and that her spared visuomotor skills are associated with visual processing in the dorsal stream.

The lateral occipital complex subserves the perceptual persistence of motion-defined groupings.

How are the bits and pieces of retinal information assembled and integrated to form the coherent objects that we see? One long-established principle is that elements that move as a group are linked together. For instance a fragmented line-drawing of an object, placed on a background of randomly distributed short lines, can be impossible to see. But if the object moves relative to the background, its shape is instantly recognized. Even after the motion stops, the percept of the object persists briefly before it fades into the background of random lines. Where in the brain does the percept of the object persist? Using functional brain imaging, we found that such moving line-drawings activated both motion-sensitive areas (medial temporal complex, MT+) and object-sensitive areas (lateral occipital complex, LOC). However, after the motion stopped only the LOC maintained its activity while the percept endured. Evidently a percept assembled by motion-sensitive areas like MT+ can be stored, at least briefly, in the LOC.

The effects of different aperture-viewing conditions on the recognition of novel objects.

The process of learning the structure of novel objects involves the selective use of information available in the distal stimulus. By allowing participants to explore the object within a limited field of view, we were able to examine more rigorously what regions of the object are actually selected in the learning process. Participants explored objects either by moving a circular aperture over a stationary novel object (the aperture-movement condition), or by moving the object behind a stationary aperture (the object-movement condition). Given the differences in how the spatial layout of object parts is revealed in the two study conditions, we expected that exploration would be more systematic in the aperture-movement condition than it would be in the object-movement condition, and would lead to better object recognition. We show evidence that in the aperture-movement condition exploration patterns were more related to the structure of the object and, as a consequence, the aperture-movement condition resulted in more accurate recognition in a later old--new discrimination test.

Differential effects of viewpoint on object-driven activation in dorsal and ventral streams.

Using fMRI, we showed that an area in the ventral temporo-occipital cortex (area vTO), which is part of the human homolog of the ventral stream of visual processing, exhibited priming for both identical and depth-rotated images of objects. This pattern of activation in area vTO corresponded to performance in a behavioral matching task. An area in the caudal part of the intraparietal sulcus (area cIPS) also showed priming, but only with identical images of objects. This dorsal-stream area treated rotated images as new objects. The difference in the pattern of priming-related activation in the two areas may reflect the respective roles of the ventral and dorsal streams in object recognition and object-directed action.

Haptic study of three-dimensional objects activates extrastriate visual areas.

In humans and many other primates, the visual system plays the major role in object recognition. But objects can also be recognized through haptic exploration, which uses our sense of touch. Nonetheless, it has been argued that the haptic system makes use of 'visual' processing to construct a representation of the object. To investigate possible interactions between the visual and haptic systems, we used functional magnetic resonance imaging to measure the effects of cross-modal haptic-to-visual priming on brain activation. Subjects studied three-dimensional novel clay objects either visually or haptically before entering the scanner. During scanning, subjects viewed visually primed, haptically primed, and non-primed objects. They also haptically explored non-primed objects. Visual and haptic exploration of non-primed objects produced significant activation in several brain regions, and produced overlapping activation in the middle occipital area (MO). Viewing visually and haptically primed objects produced more activation than viewing non-primed objects in both area MO and the lateral occipital area (LO). In summary, haptic exploration of novel three-dimensional objects produced activation, not only in somatosensory cortex, but also in areas of the occipital cortex associated with visual processing. Furthermore, previous haptic experience with these objects enhanced activation in visual areas when these same objects were subsequently viewed. Taken together, these results suggest that the object-representation systems of the ventral visual pathway are exploited for haptic object perception.