Table 1.
Characteristics of SCA patients and normal subjects.
Figure 1.
A: direction discrimination task, B: color discrimination task. In the direction discrimination task, the subject was instructed to push the button connected to the eye-tracking device as quickly as possible only when an upward-facing Landolt figure appeared at the center of monitor. In the color discrimination task, the subject was instructed to push the button only when a red Landolt figure appeared. The direction and color discrimination times were measured by the following formula: discrimination time = total time – simple reaction time.
Figure 2.
A: serial search task, B: pop-out search task. Upper panels show 4-item tasks and lower panels show 48-item tasks. In the serial search task, the subject was instructed to push the button connected to the eye-tracking device when he/she found an upward-facing Landolt figure. In the pop-out search task, the subject was instructed to push the button when he/she found a red Landolt figure. The serial and pop-out search times were measured by the following formula: search time = total time – simple reaction time.
Figure 3.
Saliency maps in search tasks.
A: serial search task, B: pop-out search task. In the pop-out search task, the target red Landolt figure is clearly colored in red, suggesting that the subjects performed bottom-up visual scanning due to the high saliency of the target. In the serial search task, high saliency areas are uniformly distributed over the images and the target upward Landolt figure is completely masked, suggesting that the subjects performed top-down visual scanning due to the low saliency of the target.
Figure 4.
Heat maps in serial search tasks.
A: SCA patients, B: normal subjects. In both 4- and 48-itemt tasks, the areas (colored areas) scanned by SCA patients were distributed more widely than those of normal subjects. The center was also colored because the starting eye-fixation position was located at the center of image.
Figure 5.
Heat maps in pop-out search tasks.
A: SCA patients, B: normal subjects. In both 4- and 48-item pop-out search tasks, the areas (colored areas) scanned by both SCA patients and normal subjects were more localized than those in serial search tasks.
Figure 6.
Eye movements in the 4-item serial search task are shown for an SCA patient (A) and a normal subject (B). In the SCA patient, the ocular fixation positions frequently did not fall exactly on the visual target, but landed at points somewhat removed from the target (saccadic dysmetria). In addition, we also observed something we term “repeated fixations (re-fixations)”. Here, the gaze initially captures the target item and then moves away before returning to the target item. To count the number of re-fixations, the target Landolt figure was selected as the region of interest.
Figure 7.
Careful visual observation of oculomotor trajectories provides information on saccadic dysmetria, repeated fixations (re-fixations) and nystagmus. These figures show recordings of the gaze trajectory during visual search (abscissa: time; ordinate: the distance of gaze position from the target (zero deg. in the abscissa corresponds to the target position) [blue curve]; and instantaneous velocity of gaze [red curve]) in an SCA patient (A) and a normal subject (B). Note that with time the gaze eventually approaches the target (distance becomes zero at the right end of each figure) but for an SCA patient it takes more time, with the gaze alternately approaching and leaving the target. After approaching the target, the gaze leaves the target once and eventually comes back to the target later (repeated fixations). In addition, the gaze position shows slow drifts, representing the slow phase of nystagmus, even during presumed fixation, whereas this rarely occurs in normal subjects.
Figure 8.
A: simple reaction time, B: direction and color discrimination time, C: serial and pop-out search time. The bars show the values of mean and standard error. Grey bars are for SCA patients and white bars for normal subjects. The simple reaction time was longer in SCA patients than in normal subjects. The direction and color discrimination time had no statistical differences. The 4- and 48-item serial search time was longer in SCA patients than in normal subjects, whereas the 4- and 48-item pop-out search time in SCA patients was almost identical to that in normal subjects. The serial search time was markedly longer than the pop-out search time in both SCA patients and normal subjects.
Table 2.
Time in all visual tasks.
Figure 9.
Visual scanning parameters in serial search tasks.
A: number of saccades, B: duration of fixation, C: amplitude of saccades, D: coefficient of variation (CV) of saccade amplitude, E: number of repeated fixations, F: instability ratio of fixation. The bars show the values of mean and standard error. Grey bars are for SCA patients and white bars for normal subjects. The number of saccades per second and duration of fixation in SCA patients were identical to those in normal subjects for both 4- and 48-item tasks. Amplitude of saccades was smaller in SCA patients than in normal subjects for both 4- and 48-item tasks, although these differences were not statistically significant. CV of saccade amplitude was larger in SCA patients than in normal subjects only in the 4-item task. Number of repeated fixations and instability ratio of fixation were larger in SCA patients than in normal subjects for both 4- and 48-item tasks.
Table 3.
Visual scanning parameters in serial search tasks.