Article Figures & Data
Figures
- Figure 1.
Experimental task. Each trial began with a flickering black and white fixation dot for 1600 ms, followed by a 500 ms blank screen. A sinusoidal grating of either high (92%) or low (2.8%) contrast and small (0.7°) or large (5.0°) size then appeared in the center of the screen. The grating drifted at a rate of 2°/s to either the left or the right; the duration of the drift was staircased to achieve ∼77% accuracy (Fig. 2). Minimum duration was set at a single 120 Hz frame refresh (8.33 ms); no maximum was set, but duration did not surpass 600 ms for any subject. Once the grating disappeared, the subject made a two-alternative forced-choice response discriminating the direction of motion. The next trial began 500 ms after the response. Trials were blocked by condition, with each block containing 150 trials. ITI, Intertrial interval.
- Figure 2.
Estimation of duration thresholds. Data from a single representative subject. For each condition, data from both staircases were combined; accuracy is plotted as a function of stimulus duration (binned into 25 ms intervals). Psychometric functions were approximated with best-fitting Weibull functions (solid lines). For each condition, duration threshold was calculated by solving the Weibull function for the stimulus duration that produced 77% accuracy (dotted lines). A, Low-contrast stimuli: the low-contrast small stimulus (gray) required a longer duration threshold than the low-contrast large stimulus (black). B, High-contrast stimuli: the high-contrast small stimulus (gray) required a shorter duration threshold than the high-contrast large stimulus (black).
- Figure 3.
Motion discrimination thresholds. Mean motion discrimination thresholds are plotted for the recovered depressed group and control group for each of the four conditions: low-contrast small, low-contrast large, high-contrast small, and high-contrast large stimuli. Thresholds were calculated by fitting the duration/accuracy data for each subject and condition with psychometric Weibull functions and determining the duration required for 77% accurate performance (Fig. 2). Higher thresholds indicate that more time was needed to reliably discriminate the direction of motion for a particular condition, implying increased difficulty perceiving the motion stimulus. Error bars are SEM.
- Figure 4.
Suppression indices. High-contrast suppression indices are plotted for each individual recovered depressed patient as a function of the total number of lifetime months the patient reported having spent depressed, a measure of MDD illness load. Suppression index was calculated as log10(high-contrast large threshold) − log10(high-contrast small threshold); positive values indicate suppression. Scatter plots were fit with the linear best-fit regression line; r = −0.51; p = 0.04; n = 16. See Results for group means.
- Figure 5.
Summation indices. Low-contrast summation indices are plotted for each individual recovered depressed patient as a function of the number of months since the patient's most recent reported depression episode, a measure of MDD recovery duration. Summation index was calculated as log10(low-contrast large threshold) − log10(low-contrast small threshold); negative values indicate summation. Scatter plots were fit with the linear best-fit regression line; r = 0.68; p = 0.004; n = 16. See Results for group means.
Tables
Healthy controls Recovered depressed p (one-way ANOVA) Gender 7 male, 9 female 7 male, 9 female 1.00 Age (years) 21.4 (2.00) 23.2 (4.25) 0.15 Decimal visual acuity 1.71 (0.31) 1.65 (0.35) 0.59 Contrast sensitivity 172.2 (48.9) 163.8 (63.3) 0.67 WRAT percentile 83.1 (12.3) 86.8 (14.8) 0.46 HAM-D 1.07 (1.58) 2.44 (2.31) 0.07* -
↵Mean (SD) for each group and significance level for between-group statistics. *Note that although the HAM-D difference trended toward significance, both groups were well within the euthymic range (<7).
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Supplemental Data
Files in this Data Supplement:
- supplemental material - Supplemental Material
