In fMRI studies, human Lateral Occipital (LO) cortex is thought to respond selectively to images of objects, compared to non-objects. However, it remains unresolved whether all objects evoke equivalent levels of activity in LO – and if not, which image features produce stronger activation. Here, we used an unbiased parametric texture model to predict preferred versus non-preferred stimuli in LO. Observation and psychophysical results showed that predicted preferred stimuli (both objects and non-objects) had smooth (rather than textured) surfaces. These predictions were confirmed using fMRI, for objects and non-objects. Similar preferences were also found in the Fusiform Face Area (FFA). Consistent with this: 1) FFA and LO responded more strongly to non-freckled (smooth) faces, compared with otherwise-identical freckled (textured) faces, and 2) strong functional connections were found between LO and FFA. Thus, LO and FFA may be part of an information-processing stream distinguished by feature-based category selectivity (smooth > textured).
Significance Statement Preferred stimuli can reveal the processing steps that take place within a given region of the visual cortex. The human Lateral Occipital (LO) cortex is thought to respond most strongly to images of objects compared to non-objects. Here, we used an unbiased computational approach to measure simple image features of object and non-object stimuli, and to generate more specific hypotheses about the optimal stimuli for LO and related visual areas. Using fMRI, we found that cortical visual areas LO and FFA respond selectively to face, object, and non-object stimuli with smooth surfaces, compared to stimuli with textured surfaces. These findings clarify visual processing steps that are performed within mid-level visual cortex.
Authors report no conflict of interest.
NIH Grant R01 EY017081