The Role of Visual and Semantic Properties in the Emergence of Category-Specific Patterns of Neural Response in the Human Brain

Brain-imaging studies have found distinct spatial and temporal patterns of response to different object categories across the brain. However, the extent to which these categorical patterns of response reflect higher-level semantic or lower-level visual properties of the stimulus remains unclear. To address this question, we measured patterns of EEG response to intact and scrambled images in the human brain. Our rationale for using scrambled images is that they have many of the visual properties found in intact images, but do not convey any semantic information. Images from different object categories (bottle, face, house) were briefly presented (400 ms) in an event-related design. A multivariate pattern analysis revealed categorical patterns of response to intact images emerged ∼80–100 ms after stimulus onset and were still evident when the stimulus was no longer present (∼800 ms). Next, we measured the patterns of response to scrambled images. Categorical patterns of response to scrambled images also emerged ∼80–100 ms after stimulus onset. However, in contrast to the intact images, distinct patterns of response to scrambled images were mostly evident while the stimulus was present (∼400 ms). Moreover, scrambled images were able to account only for all the variance in the intact images at early stages of processing. This direct manipulation of visual and semantic content provides new insights into the temporal dynamics of object perception and the extent to which different stages of processing are dependent on lower-level or higher-level properties of the image

Selectivity for mid‐level properties of faces and places in the fusiform face area and parahippocampal place area

Regions in the ventral visual pathway, such as the fusiform face area (FFA) and parahippocampal place area (PPA), are selective for images from specific object categories. Yet images from different object categories differ in their image properties. To investigate how these image properties are represented in the FFA and PPA, we compared neural responses to locally-scrambled images (in which mid-level, spatial properties are preserved) and globally-scrambled images (in which mid-level, spatial properties are not preserved). There was a greater response in the FFA and PPA to images from the preferred category relative to their non-preferred category for the scrambled conditions. However, there was a greater selectivity for locally-scrambled compared to globally-scrambled images. Next, we compared the magnitude of fMR adaptation to intact and scrambled images. fMR-adaptation was evident to locally-scrambled images from the preferred category. However, there was no adaptation to globally-scrambled images from the preferred category. These results show that the selectivity to faces and places in the FFA and PPA is dependent on mid-level properties of the image that are preserved by local scrambling

Category-selective patterns of neural response in the ventral visual pathway in the absence of categorical information

Neuroimaging studies have revealed distinct patterns of response to different object categories in the ventral visual pathway. These findings imply that object category is an important organizing principle in this region of visual cortex. However, object categories also differ systematically in their image properties. So, it is possible that these patterns of neural response could reflect differences in image properties rather than object category. To differentiate between these alternative explanations, we used images of objects that had been phase-scrambled at a local or global level. Both scrambling processes preserved many of the lower-level image properties, but rendered the images unrecognizable. We then measured the effect of image scrambling on the patterns of neural response within the ventral pathway. We found that intact and scrambled images evoked distinct category-selective patterns of activity in the ventral stream. Moreover, intact and scrambled images of the same object category produced highly similar patterns of response. These results suggest that the neural representation in the ventral visual pathway is tightly linked to the statistical properties of the image