How perceived egocentric distance varies with changes in tonic vergence

Abstract

According to the eye muscle potentiation (EMP) hypothesis, sustained vergence leads to changes in egocentric perceived distance. This perceptual effect has been attributed to a change in the resting or tonic state of vergence. The goal of the present study was to test the EMP hypothesis by quantifying the relationship between prism-induced changes in tonic vergence and corresponding changes in perceived distance and by measuring the dynamics of changes in perceived distance. During a 10-min exposure to 5-diopter base-out prisms that increased the vergence demand, thirteen right-handed subjects pointed to visual targets located within reaching space using their left hand, without visual feedback. Pre- and post-exposure tests assessed tonic vergence through phoria measurements and egocentric distance estimate through pointing to visual targets with each hand successively, without visual feedback. Similar distance aftereffects were observed for both hands, although only the left hand was used during exposure, indicating that these aftereffects are mediated by visual processes rather than by visuomotor interactions. The distance aftereffects were significantly correlated with prism-induced changes in phoria, demonstrating a relationship between perceived distance and the level of tonic vergence. Changes in perceived distance increased monotonically across trials during prism exposure and remained stable during the post-test, indicating a long time constant for these perceptual effects, consistent with current models of the vergence control system. Overall, these results support the hypothesis that vergence plays a role in reduced-cue distance perception. They further illustrate that variations in tonic vergence influence perceived distance by altering the sensed vergence effort.

Frontal eye field, where art thou? Anatomy, function, and non-invasive manipulation of frontal regions involved in eye movements and associated cognitive operations

“…Indeed, efferent copies of vergence movements, proprioception on convergence state (Priot et al, 2012), or simply disparity indices on which vergence movement can be programmed (Ziegler and Hess, 1997) are all candidates to be involved in our ability to assess depth. Conversely, our understanding of the 3D space can trigger movements in accordance with our perception.…”

(Disparity-Driven) Accommodation Response Contributes to Perceived Depth

“…As such, motor efference and/or proprioception from the vergence system are considered as sources of information for distance perception (Brenner and Van Damme, 1998). It was found that changes in vergence state using prismatic deviation consistently altered the way observers judged distance (Tresilian et al, 1999; Priot et al, 2012). Studies typically suggest that oculomotor cues to distance are only efficient in the near space, and notably in impoverished scenes (Kunnapas, 1968; Tresilian et al, 1999).…”