Short-Term Memory for Stroboscopic Movement Perception

Two-dimensional arrays of black and white random dots were generated by a computer such that features (e.g. large clusters) which could be attended to were eliminated. The first N frames were uncorrelated, but these same N frames were repeated many times. When presented at 24, 16, 12, and 8 frames/s, these movie sequences appeared as dynamic noise and subjects were tested for the longest cycle time at which they could still perceive some periodicity of motion. Subjects' judgment of seeing periodic motion decayed exponentially with the cycle duration. The time constant of this exponential was 540 ms ± 250 ms, which supports the hypothesis that memory for movement is longer than iconic memory and is about equal to echoic memory. This hypothesis has 0·94 probability of being true. At the same cycle durations, memory for stroboscopic movement also depended on N, and deteriorated for N ≥ 7.