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

Abstract

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 msec) in an event-related design. A multivariate pattern analysis (MVPA) revealed categorical patterns of response to intact images emerged ∼80-100 msec after stimulus onset and were still evident when the stimulus was no longer present (∼800 msec). Next, we measured patterns of response to scrambled images. Categorical patterns of response to scrambled images also emerged ∼80-100 msec 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 msec). Moreover, scrambled images were only able to account 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.

Significance Statement: Previous studies have shown distinct spatial and temporal patterns of response to different object categories. However, the extent to which these patterns are based on lower-level visual properties compared to high-level semantic information remains unclear. To address this question, we used scrambled objects that preserve visual properties, but do not convey any semantic information. We found distinct patterns of response to intact images from different object categories. Patterns of response to scrambled images from different categories emerge in a similar way to intact images but do not persist for the same duration. These findings demonstrate the relative importance of both lower-level visual and higher-level semantic properties in the neural response to objects.