Functional Neuroanatomy of Time-To-Passage Perception

Yansong Geng,Lucia M Vaina,Heiko Hecht,Elif Sikoglu

doi:10.4236/jbbs.2018.811039

Yansong Geng, Lucia M Vaina + Show 2 more

Open Access

https://doi.org/10.4236/jbbs.2018.811039

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Abstract

The time until an approaching object passes the observer is referred to as time-to-passage (TTP). Accurate judgment of TTP is critical for visually guided navigation, such as when walking, riding a bicycle, or driving a car. Previous research has shown that observers are able to make TTP judgments in the absence of information about local retinal object expansion. In this paper we combine psychophysics and functional MRI (fMRI) to investigate the neural substrate of TTP processing. In a previous psychophysical study, we demonstrated that when local retinal expansion cues are not available, observers take advantage of multiple sources of information to judge TTP, such as optic flow and object retinal velocities, and integrate these cues through a flexible and economic strategy. To induce strategy changes, we introduced trials with motion but without coherent optic flow (0% coherence of the background), and trials with coherent, but noisy, optic flow (75% coherence of the background). In a functional magnetic resonance imaging (fMRI) study we found that coherent optic flow cues resulted in better behavioral performance as well as higher and broader cortical activations across the visual motion processing pathway. Blood oxygen-level-dependent (BOLD) signal changes showed significant involvement of optic flow processing in the precentral sulcus (PreCS), postcentral sulcus (PostCS) and middle temporal gyrus (MTG) across all conditions. Not only highly activated during motion processing, bilateral hMT areas also showed a complex pattern in TTP judgment processing, which reflected a flexible TTP response strategy.

Highlights

In a functional magnetic resonance imaging study we found that coherent optic flow cues resulted in better behavioral performance as well as higher and broader cortical activations across the visual motion processing pathway
In this study we investigated the neural substrate of the mechanisms involved in TTP judgments in the absence of local expansion cues
Previous behavioral results suggested that the subjects base their TTP judgments on the integration of multiple sources of information, with emphasis on image cues, such as target velocity, which are supplemented by global optic flow information, if the latter is coherent

Summary

Introduction

Despite ample research on the topic, it still remains unresolved that how TTP is computed and which other optical (such as object velocity and expansion cues) are being exploited when observers are asked to provide judgments regarding the time to passage of an oncoming object. One reason why these cues have been eluding identification may lie in the adaptive nature of the visual system. When optic flow was highly coherent (75%), observers used a more complex strategy involving the global flow-field information

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