20/12/18
Speaker: Marco Gandolfo, PhD Candidate presso Bangor University
With a glimpse, we infer others’ traits based on their visual appearance, and these inferences shape our social behavior. Sex and weight are two key traits strongly cued by body shape. We found in previous work that advance knowledge of the sex of a body, provided by a verbal prime, influences the selection of visual features useful for judging body weight, and improves performance on that task. Such findings inform us about the organisation of body shape representations. Moreover, they are an example of how prior knowledge about a stimulus attribute can influence perceptual performance. A current open question relates to the neural underpinnings of such expectancy effects. Specifically, how and where does prior information (e.g. in the form of a verbal prime) influence cortical processes relevant to perception? In a first TMS experiment we addressed this question for the case of body perception. We tested whether activity in a body selective cortical region is causally involved in forming expectations about an incoming body visual stimulus. Participants judged body images as either slim or heavy. Each body was preceded by a verbal cue to its sex (80% valid, 20% invalid). Participants received online rTMS (4 pulses, 10 Hz) over functionally localized extrastriate body area (EBA) or occipital place area (OPA), starting at prime onset and ending before image onset. Stimulation over EBA, but not OPA, significantly decreased the benefit of valid cues on body size judgements. These findings elaborate the causal role of body selective EBA in processing socially relevant body shape cues. In a second experiment we addressed if the same principle applies for the case of scene perception using the same rTMS protocol but a different task. Participants judged images of scenes as either upright or inverted. Each scene was preceded by a verbal cue to its content (Kitchen/Garden, 80% valid, 20% invalid). Stimulation over OPA, but not EBA, significantly decreased the benefit of valid cues on scene orientation judgements.
These findings show that verbally-driven, content-specific expectancy effects are expressed as selective pre-activation in the occipitotemporal cortex, before stimulus onset. In this respect, they shed light on the neural basis of expectancy effects on perception in general.
Speaker’s Corner:
Alisha Vabba - "Lab Meetings: ideas for the future"