Oculomotor responses and visuospatial perceptual judgments compete for common limited resources

Abstract

While there is evidence for multiple spatial and attentional maps in the brain it is not clear to what extent visuoperceptual and oculomotor tasks rely on common neural representations and attentional mechanisms. Using a dual-task interference paradigm we tested the hypothesis that eye movements and perceptual judgments made to simultaneously presented visuospatial information compete for shared limited resources. Observers undertook judgments of stimulus collinearity (perceptual extrapolation) using a pointer and Gabor patch and/or performed saccades to a peripheral dot target while their eye movements were recorded. In addition, observers performed a non-spatial control task (contrast discrimination), matched for task difficulty and stimulus structure, which on the basis of previous studies was expected to represent a lesser load on putative shared resources. Greater mutual interference was indeed found between the saccade and extrapolation task pair than between the saccade and contrast discrimination task pair. These data are consistent with visuoperceptual and oculomotor responses competing for common limited resources as well as spatial tasks incurring a relatively high attentional cost.

Figure 1

(A) Trial sequence for Experiment 1. Observers performed perceptual extrapolation and contrast discrimination judgments on simultaneously presented visuospatial information. (B) Normalized sensitivities [expressed as a proportion of baseline (single-task) performance] for dual-task conditions. Extrapolation (white) and contrast discrimination (gray) sensitivities are shown for judgments made concurrently with the same second task (two extrapolations or two contrast discriminations), or simultaneously with a different second task (an extrapolation and a contrast discrimination), performed on distinct patches at different spatial locations. The white circle represents dual-task extrapolation performance when the second task is a contrast judgment made on the same patch (double report condition). Error bars represent the standard error of the mean (SEM).

Figure 2

Trial sequence for Experiment 2. Observers had to perform perceptual extrapolation and contrast discrimination judgments concurrently with a target-directed saccade using simultaneously presented visuospatial information.

Figure 3

Attention operating characteristic (AOC) plots showing interference effects for saccade and extrapolation (Sacc + Extrap) and saccade and contrast discrimination (Sacc + Con) task combinations. All performance levels have been normalized relative to baseline (single-task) performance. Perceptual task performance (sensitivity) is plotted along the x-axis with various measures of saccadic performance plotted along the y-axis: (A) movement onset time (Onset), (B) maximum movement velocity (Vmax), (C) landing site variable error (Error_vr) in the eccentricity domain, and (D) landing site variable error in the angular domain (Error_vθ). The cross denotes the point of independence and represents theoretical dual-task performance under conditions of zero interference. Outer data points represent single-task performance (by definition set to 1); middle points represent dual-task performance. Smaller circles and triangles represent individual data for the Sacc + Extrap and Sacc + Con conditions, respectively. Error bars (group data) represent the standard error of the mean (SEM); where not visible they are smaller than the data point.

Figure 4

Trial sequence for Experiment 3. Observers performed single-task perceptual extrapolation and contrast discrimination judgments on post-masked stimuli over a range of stimulus presentation times.

Figure 5

Perceptual extrapolation and contrast discrimination data (single task/masked stimulus) were fit with a series of power functions (solid lines) using the method of maximum likelihood estimation (MLE); the exponent terms of the best fits are presented (in brackets). Data from individual time points were also independently fit with a series of cumulative Gaussians (using MLE). Sensitivity levels (1/threshold) thus derived are also presented; error bars represent 95% confidence limits. Stim(T)—stimulus presentation time (in milliseconds).