Jacqueline C. Snow

Haptic shape processing in visual cortex

Humans typically rely upon vision to identify object shape, but we can also recognize shape via touch (haptics). Our haptic shape recognition ability raises an intriguing question: To what extent do visual cortical shape recognition mechanisms support haptic object recognition? We addressed this question using a haptic fMRI repetition design, which allowed us to identify neuronal populations sensitive to the shape of objects that were touched but not seen. In addition to the expected shape-selective fMRI responses in dorsal frontoparietal areas, we observed widespread shape-selective responses in the ventral visual cortical pathway, including primary visual cortex. Our results indicate that shape processing via touch engages many of the same neural mechanisms as visual object recognition. The shape-specific repetition effects we observed in primary visual cortex show that visual sensory areas are engaged during the haptic exploration of object shape, even in the absence of concurrent shape-related visual input. Our results complement related findings in visually deprived individuals and highlight the fundamental role of the visual system in the processing of object shape.

Real-world objects are more memorable than photographs of objects

Research studies in psychology typically use two-dimensional (2D) images of objects as proxies for real-world three-dimensional (3D) stimuli. There are, however, a number of important differences between real objects and images that could influence cognition and behavior. Although human memory has been studied extensively, only a handful of studies have used real objects in the context of memory and virtually none have directly compared memory for real objects vs. their 2D counterparts. Here we examined whether or not episodic memory is influenced by the format in which objects are displayed. We conducted two experiments asking participants to freely recall, and to recognize, a set of 44 common household objects. Critically, the exemplars were displayed to observers in one of three viewing conditions: real-world objects, colored photographs, or black and white line drawings. Stimuli were closely matched across conditions for size, orientation, and illumination. Surprisingly, recall and recognition performance was significantly better for real objects compared to colored photographs or line drawings (for which memory performance was equivalent). We replicated this pattern in a second experiment comparing memory for real objects vs. color photos, when the stimuli were matched for viewing angle across conditions. Again, recall and recognition performance was significantly better for the real objects than matched color photos of the same items. Taken together, our data suggest that real objects are more memorable than pictorial stimuli. Our results highlight the importance of studying real-world object cognition and raise the potential for applied use in developing effective strategies for education, marketing, and further research on object-related cognition.

Preserved Haptic Shape Processing after Bilateral LOC Lesions.

The visual and haptic perceptual systems are understood to share a common neural representation of object shape. A region thought to be critical for recognizing visual and haptic shape information is the lateral occipital complex (LOC). We investigated whether LOC is essential for haptic shape recognition in humans by studying behavioral responses and brain activation for haptically explored objects in a patient (M.C.) with bilateral lesions of the occipitotemporal cortex, including LOC. Despite severe deficits in recognizing objects using vision, M.C. was able to accurately recognize objects via touch. M.C.s psychophysical response profile to haptically explored shapes was also indistinguishable from controls. Using fMRI, M.C. showed no object-selective visual or haptic responses in LOC, but her pattern of haptic activation in other brain regions was remarkably similar to healthy controls. Although LOC is routinely active during visual and haptic shape recognition tasks, it is not essential for haptic recognition of object shape. SIGNIFICANCE STATEMENT The lateral occipital complex (LOC) is a brain region regarded to be critical for recognizing object shape, both in vision and in touch. However, causal evidence linking LOC with haptic shape processing is lacking. We studied recognition performance, psychophysical sensitivity, and brain response to touched objects, in a patient (M.C.) with extensive lesions involving LOC bilaterally. Despite being severely impaired in visual shape recognition, M.C. was able to identify objects via touch and she showed normal sensitivity to a haptic shape illusion. M.C.s brain response to touched objects in areas of undamaged cortex was also very similar to that observed in neurologically healthy controls. These results demonstrate that LOC is not necessary for recognizing objects via touch.

Gender-selective neural populations: evidence from event-related fMRI repetition suppression

Accurate recognition of gender in another individual is integral to successful human social interaction and to mate selection. When we encounter another person, we are effortlessly able to identify their gender, most often through the information conveyed by their facial features. Faces comprise the most abundantly encountered cue used to classify human gender. Considering the importance of facial information in gender perception, relatively little is known about the mechanisms involved in perceiving gender through human facial cues. We used an event-related fMRI repetition suppression paradigm to explore the neural circuitry underlying gender perception from facial information. Participants viewed brief consecutive images consisting of either gender-same face pairings (two male faces or two female faces) or images of gender-different face pairings (a male face preceded or followed by a female face), while attending to facial attractiveness in both conditions. Using a region-of-interest approach, we found repetition suppression on gender-same trials within the left ventral temporal fusiform gyrus and in the right collateral sulcus. Whole-brain voxel-wise analyses revealed selectivity for face gender again in the right collateral sulcus, in addition to the left cuneus and the right lateral occipital gyrus. Our results indicate that in addition to the face-selective FFA, cortical areas that are not traditionally considered to be “face-selective” are involved in the perception of gender-based facial cues.

Impaired visual sensitivity within the ipsilesional hemifield following parietal lobe damage.

The parietal cortex is considered to be part of a network of brain areas that modulates competitive interactions between targets and irrelevant distracters in early visual cortex, however there is currently little causal evidence to support this in human observers. It is also unclear as to whether parietal influences on visual perception in humans are limited to the contralesional hemispace or whether a unilateral lesion affects visual sensitivity bilaterally. Here we examined visual sensitivity in two patients with spatial neglect and extinction arising primarily from left-parietal damage. We used a sensitive psychophysical task based on those previously used to demonstrate loss of stimulus selection after lesions to extrastriate cortex. Observers discriminated the orientation of a lateralized suprathreshold target grating that appeared alone or in the context of nearby salient disc distracters. For parietal patients, target sensitivity within both the contralesional and ipsilesional fields was compromised by the presence of distracters. Conversely, healthy matched controls were unaffected by distracters. These results indicate that parietal cortex damage can influence visual perception within both the ipsi- as well as the contralesional field.

Priming tool actions: Are real objects more effective primes than pictures?

Abstract Humans are faster to grasp an object such as a tool if they have previewed the same object beforehand. This priming effect is strongest when actors gesture the use of the tool rather than simply move it, possibly because the previewed tool activates action-specific routines in dorsal-stream motor networks. Here, we examined whether real tools, which observers could physically act upon, serve as more potent primes than two-dimensional images of tools, which do not afford physical action. Participants were presented with a prime stimulus that could be either a real tool or a visually matched photograph of a tool. After a brief delay, participants interacted with a real tool target, either by ‘grasping to move,’ or ‘grasping to use’ it. The identities of the prime and target tools were either the same (congruent trials; e.g., spatula–spatula) or different (incongruent trials; e.g., whisk–spatula). As expected, participants were faster to initiate grasps during trials when they had to move the tool rather than gesture its use. Priming effects were observed for grasp-to-use, but not grasp-to-move, responses. Surprisingly, however, both pictures of tools and real tools primed action responses equally. Our results indicate that tool priming effects are driven by pictorial cues and their implied actions, even in the absence of volumetric cues that reflect the tangibility and affordances of the prime.

Graspable Objects Grab Attention More Than Images Do

The opportunity an object presents for action is known as an affordance. A basic assumption in previous research was that images of objects, which do not afford physical action, elicit effects on attention and behavior comparable with those of real-world tangible objects. Using a flanker task, we compared interference effects between real graspable objects and matched 2-D or 3-D images of the items. Compared with both 2-D and 3-D images, real objects yielded slower response times overall and elicited greater flanker interference effects. When the real objects were positioned out of reach or behind a transparent barrier, the pattern of response times and interference effects was comparable with that for 2-D images. Graspable objects exert a more powerful influence on attention and manual responses than images because of the affordances they offer for manual interaction. These results raise questions about whether images are suitable proxies for real objects in psychological research.

Action properties of object images facilitate visual search.

There is mounting evidence that constraints from action can influence the early stages of object selection, even in the absence of any explicit preparation for action. Here, we examined whether action properties of images can influence visual search, and whether such effects were modulated by hand preference. Observers searched for an oddball target among 3 distractors. The search arrays consisted either of images of graspable “handles” (“action-related” stimuli), or images that were otherwise identical to the handles but in which the semicircular fulcrum element was reoriented so that the stimuli no longer looked like graspable objects (“non-action-related” stimuli). In Experiment 1, right-handed observers, who have been shown previously to prefer to use the right hand over the left for manual tasks, were faster to detect targets in action-related versus non-action-related arrays, and showed a response time (reaction time [RT]) advantage for rightward- versus leftward-oriented action-related handles. In Experiment 2, left-handed observers, who have been shown to use the left and right hands relatively equally in manual tasks, were also faster to detect targets in the action-related versus non-action-related arrays, but RTs were equally fast for rightward- and leftward-oriented handle targets. Together, or results suggest that action properties in images, and constraints for action imposed by preferences for manual interaction with objects, can influence attentional selection in the context of visual search.

Preserved Object Weight Processing after Bilateral Lateral Occipital Complex Lesions

Object interaction requires knowledge of the weight of an object, as well as its shape. The lateral occipital complex (LOC), an area within the ventral visual pathway, is well known to be critically involved in processing visual shape information. Recently, however, LOC has also been implicated in coding object weight before grasping—a result that is surprising because weight is a nonvisual object property that is more relevant for motor interaction than visual perception. Here, we examined the causal role of LOC in perceiving heaviness and in determining appropriate fingertip forces during object lifting. We studied perceptions of heaviness and lifting behavior in a neuropsychological patient (M.C.) who has large bilateral occipitotemporal lesions that include LOC. We compared the patients performance to a group of 18 neurologically healthy age-matched controls. Participants were asked to lift and report the perceived heaviness of a set of equally weighted spherical objects of various sizes—stimuli which typically induce the size–weight illusion, in which the smaller objects feel heavier than the larger objects despite having identical mass. Despite her ventral stream lesions, M.C. experienced a robust size–weight illusion induced by visual cues to object volume, and the magnitude of the illusion in M.C. was comparable to age-matched controls. Similarly, M.C. evinced predictive fingertip force scaling to visual size cues during her initial lifts of the objects that were well within the normal range. These single-case neuropsychological findings suggest that LOC is unlikely to play a causal role in computing object weight.

Towards a unified perspective of object shape and motion processing in human dorsal cortex

Although object-related areas were discovered in human parietal cortex a decade ago, surprisingly little is known about the nature and purpose of these representations, and how they differ from those in the ventral processing stream. In this article, we review evidence for the unique contribution of object areas of dorsal cortex to three-dimensional (3-D) shape representation, the localization of objects in space, and in guiding reaching and grasping actions. We also highlight the role of dorsal cortex in form-motion interaction and spatiotemporal integration, possible functional relationships between 3-D shape and motion processing, and how these processes operate together in the service of supporting goal-directed actions with objects. Fundamental differences between the nature of object representations in the dorsal versus ventral processing streams are considered, with an emphasis on how and why dorsal cortex supports veridical (rather than invariant) representations of objects to guide goal-directed hand actions in dynamic visual environments.