Does Area V3A Predict Positions of Moving Objects?

Abstract

A gradually fading moving object is perceived to disappear at positions beyond its luminance detection threshold, whereas abrupt offsets are usually localized accurately. What role does retinotopic activity in visual cortex play in this motion-induced mislocalization of the endpoint of fading objects? Using functional magnetic resonance imaging (fMRI), we localized regions of interest (ROIs) in retinotopic maps abutting the trajectory endpoint of a bar moving either toward or away from this position while gradually decreasing or increasing in luminance. Area V3A showed predictive activity, with stronger fMRI responses for motion toward versus away from the ROI. This effect was independent of the change in luminance. In Area V1 we found higher activity for high-contrast onsets and offsets near the ROI, but no significant differences between motion directions. We suggest that perceived final positions of moving objects are based on an interplay of predictive position representations in higher motion-sensitive retinotopic areas and offset transients in primary visual cortex.

Keywords: V1; V3A; fMRI; localization; prediction; visual motion.

Figure 1

(A) Illustration of the moving stimuli. All motion was smooth, only “snapshots” at different time points of the trajectory are shown here. In the low-contrast offset condition (lc-off) a radial bar appeared at the 12 o'clock position and moved smoothly in a clockwise direction around the fixation point, while gradually fading. At the 3 o'clock position, on the horizontal meridian, it vanished. Oppositely, the low-contrast onset stimulus (lc-on) started moving from the 3 o'clock position and gradually increased in contrast until the 12 o'clock position, where it disappeared abruptly. These two conditions had weak transients near the region of interest just below the horizontal meridian. (B) In the other two conditions (hc-off and hc-on) the moving bar had high-contrast onsets/offsets at the horizontal meridian. (C) The checkerboard conditions were used as localizers to identify ROIs just below and just above the horizontal meridian. All three conditions are shown here (cb-up, cb-mid, cb-low), although only one checkerboard was presented in any given trial.

Figure 2

The mean perceived offset and onset positions from the psychophysics experiment outside of the MRI scanner (n = 5). A low-contrast offset (lc-off) leads to a perceived overshoot, high-contrast offsets (hc-off) are perceived accurately. Onsets are mislocalized forward in the direction of motion, the well-documented Fröhlich effect. Error bars are standard errors of the mean.

Figure 3

The ROIs in the left hemisphere of two participants. The view is on the occipital pole of “inflated” cortices. Blue-turquoise areas show positive, yellow-orange negative RC values (positive RC values are retinotopic positions below the horizontal meridian). The circled areas show the selected ROIs in V1 (in the Calcarine sulcus), along the V2/V3 border in dorsal and ventral cortex, and in V3A.

Figure 4

(A) BOLD time courses (as reconstructed by a fixed-effects deconvolution GLM) in response to the four motion conditions and fitted gamma-functions. (B) Sum of beta values from the deconvolution GLM in a time window 3–8 s after stimulus onset. (C) Area under curve as an index of BOLD response magnitude.