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Functional Neuroanatomy of Time-To-Passage Perception

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. 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.

In this paper, the authors combined psychophysics and functional MRI (fMRI) to investigate the neural substrate of TTP processing. Seven subjects (5 females, 2 males, mean age = 24.42 years old, SD = 4.82 years) participated in the study. All of them had normal or corrected-to-normal vision. The stimuli were generated on an Intel-based Macintosh laptop and displayed at a resolution of 1024 × 768 pixels and a refresh rate of 75 Hz. Two of the dots, referred to as target dots, were red (51.20 cd/m2) and the rest of them were white (79.55 cd/m2), all displayed against a gray background (10.22 cd/m2). Subjects viewed the translucent screen through a mirror mounted on the head coil of a whole-body scanner. fMRI data were acquired at Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital, using a 3T Siemens whole body scanner and a standard 8-channel head coil.

Imaging data analysis was performed using the Statistical Parametric Mapping software package (SPM12, Wellcome Department of Cognitive Neurology, London, UK) and utilizing MATLAB (The MathWorks, Natick, Massachusetts, USA). For each subject, the onset and duration of each condition was modeled by a general linear model (GLM).

The results showed that across all the subjects, the activation areas were distributed along the motion processing pathway. And the activation was not only showing along the ventral pathway , it also showed along the dorsal pathway. Activation during the stimulus motion was significantly elevated compared to baseline in the occipital lobe, including the superior occipital gyrus (SOG), temporal lobe including middle temporal gyrus (MTG), inferior temporal gyrus (ITG) and superior temporal sulcus (STS), parietal lobe including superior parietal gyrus (SPG) and intraparietal sulcus (IPS), frontal lobe including middle frontal gyrus (MFG) and inferior frontal gyrus (IFG). The percent signal changes suggest that bilateral precentral and postcentral sulci as well as a MTG are highly involved in the processing of global optic flow.

In conclusion, the fMRI results show a broad range of activation along the visual motion processing pathway, which reflects the complex information processing strategy.


Article by Yansong Geng, et al, from USA and Germany.

Full access: http://mrw.so/4y7MDN

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