Manan P. Shah

Greater sensitivity to nonaccidental than metric shape properties in preschool children.

Nonaccidental properties (NAPs) are image properties that are invariant over orientation in depth and allow facile recognition of objects at varied orientations. NAPs are distinguished from metric properties (MPs) that generally vary continuously with changes in orientation in depth. While a number of studies have demonstrated greater sensitivity to NAPs in human adults, pigeons, and macaque IT cells, the few studies that investigated sensitivities in preschool children did not find significantly greater sensitivity to NAPs. However, these studies did not provide a principled measure of the physical image differences for the MP and NAP variations. We assessed sensitivity to NAP vs. MP differences in a nonmatch-to-sample task in which 14 preschool children were instructed to choose which of two shapes was different from a sample shape in a triangular display. Importantly, we scaled the shape differences so that MP and NAP differences were roughly equal (although the MP differences were slightly larger), using the Gabor-Jet model of V1 similarity (Lades & et al., 1993). Mean reaction times (RTs) for every child were shorter when the target shape differed from the sample in a NAP than an MP. The results suggest that preschoolers, like adults, are more sensitive to NAPs, which could explain their ability to rapidly learn new objects, even without observing them from every possible orientation.

A neurocomputational account of the face configural effect

A striking phenomenon in face perception is the configural effect in which a difference in a single part appears more distinct in the context of a face than it does by itself. The face context would be expected to increase search complexity, rendering discrimination more--not less--difficult. Remarkably, there has never been a biologically plausible explanation of this fundamental signature of face recognition.We show that the configural effect can be simply derived from a model composed of overlapping receptive fields (RFs) characteristic of early cortical simple-cell tuning but also present in face-selective areas. Because of the overlap in RFs, the difference in a single part is not only represented in the RFs centered on it but also propagated to larger RFs centered on distant parts of the face. Dissimilarity values computed from the model between pairs of faces and pairs of face parts closely matched the recognition accuracy of human observers who had learned a set of faces composed of composite parts and were tested on wholes (Which is Larry?) and parts (Which is Larry’s nose?). When stimuli were high versus low passed the contributions of different spatial frequency (SF) bands to the configural effect were largely comparable. Therefore, it was the larger RFs rather than the low SFs that accounted for most of the configural effect. The representation explains why, relative to objects, face recognition is so adversely affected by inversion and contrast reversal and why distinctions between similar faces are ineffable.

The Lateral Occipital Complex shows no net response to object familiarity.

In 1995, Malach et al. discovered an area whose fMRI BOLD response was greater when viewing intact, familiar objects than when viewing their scrambled versions (resembling texture). Since then hundreds of studies have explored this late visual region termed the Lateral Occipital Complex (LOC), which is now known to be critical for shape perception (James, Culham, Humphrey, Milner, & Goodale, 2003). Malach et al. (1995) discounted a role of familiarity by showing that “abstract” Henry Moore sculptures, unfamiliar to the subjects, also activated this region. This characterization of LOC as a region that responds to shape independently of familiarity has been accepted but never tested with control of the same low-level features. We assessed LOCs response to objects that had identical parts in two different arrangements, one familiar and the other novel. Malach was correct: There is no net effect of familiarity in LOC. However, a multivoxel correlation analysis showed that LOC does distinguish familiar from novel objects.

Barriers to use of oral rehydration salts for child diarrhea in the private sector: evidence from India

Diarrhea is the second leading cause of child mortality in India. Most deaths are cheaply preventable with the use of oral rehydration salts (ORS), yet many health providers still fail to provide ORS to children seeking diarrheal care. In this study, we use survey data to assess whether children visiting private providers for diarrheal care were less likely to use ORS than those visiting public providers. Results suggest that children who visited private providers were 9.5 percentage points less likely to have used ORS than those who visited public providers (95% CI 5-14). We complimented these results with in-depth interviews of 21 public and 17 private doctors in Gujarat, India, assessing potential drivers of public-private disparities in ORS use. Interview results suggested that lack of direct medication dispensing in the private sector might be a key barrier to ORS use in the private sector.

A neurocomputational account of the magnitude of face composite effects.

Identical top halves of two faces are more likely to be perceived as different when their different bottom halves are aligned rather than offset. Here, we demonstrate that the magnitude of the offset effect for each face can be predicted from a model of overlapping receptive fields with tuning profiles similar to the hypercolumns of simple cells in V1, although the cells are likely in face-selective areas. Importantly, a single face part (e.g. the left eye) is coded by multiple large receptive fields centered at a distance from the face part (Fig. 1). When different bottom halves are aligned to the identical top halves of faces, the large receptive fields centered on the top half of the face will extend to the differing bottom halves, thus making the top halves of the faces more dissimilar. By offsetting the differing bottom halves from the identical top halves of two faces, the features of the bottom halves no longer activate the large receptive fields centered on the top half of the face, leading to more accurate judgments of the identical top halves as the same (Fig. 2). The retention of early-level visual coding (Yue, Tjan, & Biederman, 2006; Xu, Biederman, & Shah, 2014) and the retinotopic representation of a face template in FFA (de Haas et al., 2014) may explain why the offset effect is unique to faces rather than the parts-based representation of objects. Meeting abstract presented at VSS 2015.

What Is Actually Affected by the Scrambling of Objects When Localizing the Lateral Occipital Complex

The lateral occipital complex (LOC), the cortical region critical for shape perception, is localized with fMRI by its greater BOLD activity when viewing intact objects compared with their scrambled versions (resembling texture). Despite hundreds of studies investigating LOC, what the LOC localizer accomplishes—beyond distinguishing shape from texture—has never been resolved. By independently scattering the intact parts of objects, the axis structure defining the relations between parts was no longer defined. This led to a diminished BOLD response, despite the increase in the number of independent entities (the parts) produced by the scattering, thus indicating that LOC specifies interpart relations, in addition to specifying the shape of the parts themselves. LOCs sensitivity to relations is not confined to those between parts but is also readily apparent between objects, rendering it—and not subsequent “place” areas—as the critical region for the representation of scenes. Moreover, that these effects are witnessed with novel as well as familiar intact objects and scenes suggests that the relations are computed on the fly, rather than being retrieved from memory.

Coding of Visual Stimuli for Size and Animacy

Blocked presentations of objects (Small-Large Crossed w. AnimalsObjects). Subjects performed an oddball (red bounding box aroud image) detection task. Mean referential size of was comparable between animals and objects (Object size from Konkle & Oliva, 2011; Animals fromWikipedia). Animacy: Animals activated ventral lateral temporal cortex, while inanimate objects activated more medial regions of the ventral temporal lobe, and dorsal occipital lobe.