Separate timescales for spatial and anatomical information processing of body stimuli

Observing different body stimuli can influence the speed and accuracy of our responses. Prior work indicates this effect is influenced by factors such as spatial congruence and perspective. We hypothesized that the influence of these factors would vary depending on the amount of time that participants had to process visual stimuli. Experiment 1 was a reaction time task (n=29) with stimuli varying in spatial congruence (congruent, incongruent, neutral), perspective (first- or third-person) and stimulus type (body or control). Experiment 2 (n=50) used the same stimuli in a “Forced Response” paradigm, which controlled the time participants had to prepare a response. This allowed us to assess responses as a function of preparation time. Experiment 1 showed effects of spatial congruence, with longer reaction times and more errors for spatially incongruent stimuli. This effect was greater for body stimuli. Experiment 2 showed that spatial information was processed faster than anatomical information, inducing incorrect responses at short preparation times for spatially incongruent body stimuli. There was little-to-no corresponding effect for control stimuli. Both experiments also showed weak-to-no effects of perspective, which appear to have been driven by spatial congruence. Our results indicate that spatial information is processed faster than anatomical information during observation of body stimuli. These data are consistent with the dual visual streams hypothesis, whereby spatial information would be processed rapidly via the dorsal stream, while anatomical processing would occur later via the ventral stream. These data also indicate differences in processing between body and control stimuli.