The contribution of amplitude and phase spectra-defined scene statistics to the masking of rapid scene categorization.

Viewers can recognize the gist of a scene (i.e., its holistic semantic representation, such as its category) in less time than a single fixation, and backward masking has traditionally been employed as a means to determine that time course. The masks used in those paradigms are often characterized by either specific amplitude spectra only, or amplitude and phase spectra-defined structural properties. However, it remains unclear whether there would be a differential contribution of amplitude only or amplitude + phase defined image statistics to the effective backward masking of rapid scene categorization. The current study addresses this issue. Experiments 1-3 explored amplitude spectra defined contributions to category masking and revealed that the slope of the amplitude spectrum was more important for modulating scene category masking strength than amplitude orientation. Further, the masking effects followed an "amplitude spectrum slope similarity principle" whereby the more similar the amplitude spectrum slope of the mask was to the target's amplitude spectrum slope, the stronger the masking. Experiment 5 showed that, when holding mask amplitude spectrum slope approximately constant, both categorically specific unrecognizable amplitude only and amplitude + phase statistical regularities disrupted rapid scene categorization. Specifically, the masking effects observed in Experiment 5 followed a target-mask categorical dissimilarity principle whereby the more dissimilar the mask category is to the target image category, the stronger the masking. Overall, the results support the notion that amplitude only or amplitude + phase-defined image statistics differentially contribute to the effective backward masking of rapid scene gist recognition.