Hemispheric functional asymmetries and sex effects in visual bistable perception.

Bistable perception of ambiguous figures differs by sex and by which visual hemifield the stimulus is presented to, suggesting hemispheric asymmetries in conscious perception. In two experiments, 48 participants viewed Rubin's vase-faces figures projected to either the left and right or upper and lower visual hemifields for 180 seconds while eye movements were tracked. In the first experiment, males perceived face profiles for longer when stimuli were presented to the left visual field (processed by the right hemisphere) and the vase for longer in the right visual field, while females showed similar perception across hemifields. Males also more often experienced two different percepts simultaneously from identical stimuli. These effects were absent when stimuli were presented to upper and lower fields.

Study at a glance

Abstract

This study investigates bistable perception as a function of the presentation side of the ambiguous figures and of participants' sex, to evaluate left-right hemispheric (LH-RH) asymmetries related to consciousness. In two experiments using the divided visual field paradigm, two Rubin's vase-faces figures were projected simultaneously and continuously 180 s long to the left (LVF) and right (RVF; Experiment 1) or to the upper (UVF) and lower (DVF; Experiment 2) visual hemifields of 48 healthy subjects monitored with eye-tracker. Experiment 1 enables stimulus segregation from the LVF to the RH and from the RVF to the LH, whereas Experiment 2 does not. Results from Experiment 1 show that males perceived the face profiles for more time in the LVF than in the RVF, with an opposite trend for the vase, whereas females show a similar pattern of perception in the two hemifields. A related result confirmed the previously reported possibility to have simultaneously two different percepts (qualia) in the two hemifields elicited by the two identic ambiguous stimuli, which was here observed to occur more frequently in males. Similar effects were not observed in Experiment 2. These findings suggest that the percepts display the processing abilities of the hemisphere currently processing the stimulus eliciting them (e.g., RH-faces), and that females and males reflect in bistable perception, a genuine manifestation of consciousness, the well-known hemispheric asymmetry differences they show in ordinary perception.