Threat modulates perception of looming visual stimuli

Abstract

Objects on a collision course with an observer produce a specific pattern of optical expansion on the retina known as looming, which in theory exactly specifies time-to-collision. Looming stimuli produce stereotyped defensive responses in monkeys and human infants, indicating that the primate visual system is intrinsically tuned to interpret this stimulus as threatening. We investigated how emotional reactions to the semantic content of a looming stimulus affects perceived time-to-collision. We presented either threatening (snakes, spiders) or non-threatening (butterflies and rabbits) stimuli which expanded in size at a rate indicating one of five different times to contact (3.0, 3.5, 4.0, 4.5 or 5.0 s). After 1 s, the image disappeared and participants judged when it would have made contact with them continuing on the same trajectory. Consistent with previous findings, time-to-collision judgments systematically underestimated true arrival time. More importantly, our results showed that the magnitude of this underestimating significantly increased for threatening, compared to non-threatening, stimuli. Further, the magnitude of this increase was correlated with participants’ self-reported fear of snakes and spiders. Traditionally, looming has been interpreted as a purely optical cue to collision. Against that view, our results demonstrate that the semantic content of visual stimuli modulates perceived time-to-contact. Our results suggest that perceived threat led participants to use a larger margin of safety: underestimating time-to-collision errs on the side of allowing more time to prepare defensive responses (or flee). More generally, these results demonstrate that emotion has widespread effects on even very basic aspects of perception.

Threat modulates neural responses to looming visual stimuli

“…Stimuli were the same as used in the previous study (Vagnoni et al ., ), namely 160 colour photographs collected from the internet, 40 from each of the four categories. Images were cropped and resized using Adobe Photoshop CS5 (Adobe Systems, San Jose, CA, USA).…”

“…The width of the stimulus on the first frame was either 400 or 500 pixels (15.1° or 18.9° visual angle), giving the impression that it was at two different distances. It seems, from the previous results (Vagnoni et al ., ), that participants judged bigger stimuli as closer and smaller as farther. It cannot be excluded, however, that the stimuli were perceived of different size and at the same distance.…”

“…Fear ratings for each of the four categories were collected by modifying the Fear of Spiders Questionnaire (Szymanski & O'Donohue, ), as in the previous study (Vagnoni et al ., ). The 18 items on this questionnaire ask participants to indicate their agreement or disagreement with statements indicating fear or anxiety related to spiders.…”

“…In contrast, two recent studies have demonstrated that perceived TTC is affected by the semantic content of looming stimuli (Brendel et al ., ; Vagnoni et al ., ). In the study of Vagnoni et al ., participants completed a TTC task in which a visual stimulus expanded in size over 1 s and then disappeared.…”

“…threatening, non‐threatening) were manipulated. The authors' previous work showed that threat influences looming judgements, with the arrival time of threatening images underestimated relative to non‐threatening images (Vagnoni et al ., ). This study investigates the neural basis of this underestimation effect of threatening stimuli.…”