Perceptual learning of motion leads to faster flicker perception

Abstract

Critical flicker fusion thresholds (CFFT) describe when quick amplitude modulations of a light source become undetectable as the frequency of the modulation increases. The threshold at which CFF occurs has been shown to remain constant under repeated testing. Additionally, CFF thresholds are correlated with various measures of intelligence, and have been regarded by clinicians as a general measure of cortical processing capacity. For these reasons, CFF is used as a cognitive indicator in drug studies, as a measure of fatigue, and has been suggested as a diagnostic measure for various brain diseases. Here we report that CFFT increases dramatically in subjects who are trained with a motion-direction learning procedure. Control tasks demonstrate that CFFT changes are tightly coupled with improvements in discriminating the direction of motion stimuli, and are likely related to plasticity in low-level visual areas that are specialized to process motion signals. This plasticity is long-lasting and is retained for at least one year after training. Combined, these results show that CFFT relates to a specialized sensory process and bring into question that CFFT is a measure of high-level, or general, processes.

Figure 1. Experiment Design.

For each group a direction discrimination test was performed before and after 9 days of training and CFFT was measured at the beginning of each training session. In Direction-Training, subjects reported two-targets (shown in white) at the end of the trial and a specific direction of motion was paired with task-targets. In No-Motion training, task was the same, but no dots were displayed. In No-Coherence training, task was the same but dots all moved randomly. In N-Back training, task was to report if a letter was repeated twice in a trial (in this case the L; shown in white for graphic purposes), there was no relationship between task-targets and motion directions.

Figure 2. CFFT increases from Direction-Training.

a, CFFT are shown for each day for the Direction-Training Group (solid-line) and the Flicker-Only Group (dashed-line). b, pre-training, post-training, and 1-year post-training results for subjects in the Direction-Training group who were re-tested 1-year after the conclusion of the training procedure. Error bars reflect standard-error.

Figure 3. Motion-direction sensitivity change from Direction Training.

a, performance for paired-direction on pre-test (dashed-line) and post-test (solid-line). b, performance for averaged across non-paired directions on pre-test (dashed-line) and post-test (solid-line). Error bars reflect standard-error.

Figure 4. CFFT changes for control groups.

a, CFFT is shown for each day for the No-Motion Group (solid-line) and the Flicker-Only Group (dashed-line). b, CFFT is shown for each day for the No-Coherence Group (solid-line) and the Flicker-Only Group (dashed-line). a, CFFT is shown for each day for the N-Back Group (solid-line) and the Flicker-Only Group (dashed-line). Error bars reflect standard-error.

Figure 5. CFFT increases and motion-direction sensitivity for control groups.

a, Histogram of percent-change in CFFT for subjects in the No-Motion, No-Coherence, N-Back and N-Back-0% Groups. b, performance averaged across directions for Flicker-Learning subjects on pre-test (dashed-line) and post-test (solid-line). b, performance averaged across directions for Flicker-Stable subjects on pre-test (dashed-line) and post-test (solid-line). Error bars reflect standard-error.