Cardiovascular Measures of Attention to Illusory and Nonillusory Visual Stimuli

This study was an extension of the Berntson, Cacioppo, and Fieldstone (1996) study that found that attending to visual illusions presented with text (usually a question directing attention to the illusory property) lengthened heart period via uncoupled vagal activation. Eighty participants were assigned to one of four groups that received either the original Berntson et al. illusions or a modification formed by the factorial combination of whether the illusion and its related text were present or absent. Participants also performed the same serial-subtraction mental-arithmetic task from Berntson et al. During the mental-arithmetic task heart period (HP) shortened, respiratory sinus arrhythmia (RSA) was reduced, and preejection period (PEP) shortened, which indicated a reciprocally coupled sympathetic activation and parasympathetic inhibition mode of cardiac control. Although idiographic analyses found this to be the most common control mode, all other modes were also obtained – especially the nonreciprocal modes of coactivation and coinhibition. During the visual task, PEP lengthened for all groups indicating uncoupled sympathetic inhibition while attending to the stimuli; however, HP differed depending upon the illusion factor. HP lengthened when illusions were absent, but unlike Berntson et al. it shortened when illusions were present. Idiographic analyses found that although most participants showed sympathetic inhibition, approximately equal numbers of participants showed parasympathetic activation and inhibition. Variation in response stereotypy may mask cardiac responses elicited by subtle cognitive phenomena such as the processing of visual illusions, especially in passive viewing tasks. We also suggest that individual differences in mental effort needed to integrate top-down and bottom-up perceptual processes, or personality variables such as the need for cognition, may contribute to response variability in the visual task.