Implicit Learning of Temporal Discriminations in Perception

Abstract

We measured the temporal accuracy of signal transfer in the brain by means of periodic pulse stimuli in various sensory modalities using an adaptive threshold algorithm. Trains of supra-threshold signal pairs in 0° or 180° phase shifts appeared, and the subject indicated whether the signals of each pair in a train were simultaneous or not at various nominal frequencies of the pairs. The signals were spatially separate flashes of light, clicks, tactile pulses, or combinations thereof in intermodal comparisons. Temporal discrimination thresholds involving one signal in central photopic vision and the other in audition or tactile presentation to the finger tips did not exceed frequencies from 3 to 8 Hz, and in vision alone the average synchronism thresholds were about 10 Hz (SOA 0.05 s with 0.008 s pulses). The practice derived from 9 experimental sessions during 6 weeks improved temporal accuracy by factors ranging from 1.2 to 2.0 on the average in a sample of 33 naive subjects (university students), although no explicit feedback was given. The practice effect was lasting, for the average performance decrement was only 9% in 7 months. Thus, a considerable temporal modifiability must exist in the brain because a large learning effect was found in the simple temporal synchronism discrimination tasks.