Parsing pulses: testing the limits of temporal phase perception in human vision
Date
2025
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Publisher
University of Delaware
Abstract
Complete information about temporal visual stimuli is available to human conscious awareness at frequencies below about 10 Hz, a threshold known as the Gestalt Flicker Frequency threshold. At faster frequencies, approximately 10–60 Hz, flicker is perceived but the accurate discrimination of temporal phase is not possible. Above about 60 Hz, the Critical Flicker Fusion frequency, stimuli are completely fused and not perceived as temporally varying. To accurately measure temporal phase limits, care must be taken to avoid activating low-level mechanisms that might invoke a perception of motion, which could bely temporal phase. This study explores the temporal properties and neural mechanisms underlying phase discrimination in human vision by examining the impact of interstimulus spacing and hemifield placement on temporal frequency thresholds in a paired achromatic flicker task. Experiment 1 was conducted with binocular viewing and found that narrow interstimulus spacing resulted in higher phase discrimination thresholds, suggesting contributions from low-level motion detection. Wide spacing relied on high-level processing, which led to reduced thresholds. Experiment 2 utilized dichoptic viewing to assess whether low-level motion detection occurs before binocular combination in V1, with findings showing reduced thresholds irrespective of spacing, suggesting that low-level mechanisms were successfully disabled with dichoptic viewing, and that discriminations were instead performed by high-level mechanisms in higher-order cortical areas. Despite the wide range of stimuli that jointly activate these mechanisms due to their overlapping temporal ranges, these results reveal that apparent motion and high-level processing appear to work independently. Once apparent motion is eliminated, thresholds drop to 7–10 Hz. ☐ Keywords: temporal phase discrimination; flicker fusion; psychophysics; visual perception; binocular vision; dichoptic vision; apparent motion
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Keywords
Binocular vision, Dichoptic vision, Flicker fusion, Psychophysics, Temporal phase discrimination, Visual perception