Gaze patterns during presentation of fixed and random phase radial frequency patterns

Abstract

Radial frequency (RF) patterns, circles which have had their radius modulated as a function of their polar angle, have been used in the examination of the integration of contour information around closed contour patterns. Typically, these patterns have been presented in a random orientation from trial-to-trial in order to maintain spatial uncertainty as to the location of the deformation on the pattern, as it may affect observer strategy and performance. However, the effect of fixed and random orientation (phase) on observer gaze strategies used to discriminate RF patterns has not been directly tested. This study compared fixation patterns across four conditions: fixed phase single cycle; random phase single cycle; fixed phase three cycle; and random phase three cycle RF3 patterns. The results showed that observers fixated on the known location of deformation for the fixed phase single cycle condition but used a more central fixation for the other three conditions. This strategy had a significant effect on observer thresholds for the fixed phase single cycle condition, with greater adherence to the strategy resulting in lower thresholds. It was also found that for the single cycle patterns observers tended to fixate on different locations on the pattern: on the maximum orientation difference from circular for the fixed phase pattern; and on the point of maximum curvature for the random phase pattern. These differences in gaze patterns are likely driven by the underlying local or global processing of the fixed or random phase single cycle patterns, respectively.

Figure 1

. Task paradigm. Note that fixation cross is only present at the beginning of the trial.

Figure 2.

Left, RF3(1) and right, RF3. Both patterns are presented in the orientation shown for the fixed phase condition.

Figure 3.

Geometric means with 95% confidence intervals of observer thresholds for fixed (red) and random (black) phase conditions at one and three cycles of modulation.

Figure 4.

Peakedness of observer fixations for all four conditions with 95% confidence intervals.

Figure 5.

Heatmaps of fixation locations for random phase (left) and fixed phase (right) single cycle RF3s. The fixation locations are binned in π/10 radian segments and contain the total number of observers with their overall fixation vector for that condition within that bin. The white arrow shows the vector sum of all the observer fixations during stimulus presentation. The data shows that observers display different fixation locations depending on whether the pattern is fixed or random phase.

Figure 6.

Mean polar angles and peakedness for fixational eye movements occurring during the presentation of the reference stimulus in either the first or second interval. The fixed phase condition at 1 cycle of modulation clearly displays different fixational eye movements in comparison to the other three conditions.

Figure 7.

Box and whisker plots of the overall peakedness of fixational eye movements during the presentation of the reference stimulus.