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Perceived duration of brief visual events is mediated by timing mechanisms at the global stages of visual processing

View Article: PubMed Central - PubMed

ABSTRACT

There is a growing body of evidence pointing to the existence of modality-specific timing mechanisms for encoding sub-second durations. For example, the duration compression effect describes how prior adaptation to a dynamic visual stimulus results in participants underestimating the duration of a sub-second test stimulus when it is presented at the adapted location. There is substantial evidence for the existence of both cortical and pre-cortical visual timing mechanisms; however, little is known about where in the processing hierarchy the cortical mechanisms are likely to be located. We carried out a series of experiments to determine whether or not timing mechanisms are to be found at the global processing level. We had participants adapt to random dot patterns that varied in their motion coherence, thus allowing us to probe the visual system at the level of motion integration. Our first experiment revealed a positive linear relationship between the motion coherence level of the adaptor stimulus and duration compression magnitude. However, increasing the motion coherence level in a stimulus also results in an increase in global speed. To test whether duration compression effects were driven by global speed or global motion, we repeated the experiment, but kept global speed fixed while varying motion coherence levels. The duration compression persisted, but the linear relationship with motion coherence was absent, suggesting that the effect was driven by adapting global speed mechanisms. Our results support previous claims that visual timing mechanisms persist at the level of global processing.

No MeSH data available.


(a) Experimental timeline. (b) Change in perceived duration as a function of the adaptor coherence level. Negative and positive values indicate duration compression and duration expansion, respectively. It is clear that increasing the adaptor's motion coherence level leads to a concomitant increase in the magnitude of the duration compression effect (error bars are ±1 s.e.).
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RSOS160928F1: (a) Experimental timeline. (b) Change in perceived duration as a function of the adaptor coherence level. Negative and positive values indicate duration compression and duration expansion, respectively. It is clear that increasing the adaptor's motion coherence level leads to a concomitant increase in the magnitude of the duration compression effect (error bars are ±1 s.e.).

Mentions: Observers adapted for 30 s to a moving random dot pattern centred 5° left of a central fixation point, in which each dot moved at the same speed 3° s−1 (figure 1a). Observers maintained fixation throughout each block of trials. Within each block of trials the adaptor pattern was assigned a fixed motion coherence value of 0%, 20%, 40%, 60%, 80% or 100%. The lifetime of each dot was set to the duration of the adaptor stimulus. In the case of 100% motion coherence all dots in the adaptor stimulus drifted upwards; for lower motion coherence levels the probability that a dot was assigned the signal motion direction (upwards) on each frame was determined by the motion coherence parameter. Thus, for the 20% motion coherence condition each dot had a 0.2 probability of being assigned the signal motion direction, and a 0.8 probability of being assigned a random motion direction, on a given frame. Using the terminology of Scase et al. [24], who looked at motion thresholds for a variety of different types of RDK, our random dot pattern is classified as random walk using the different rule. After 30 s adaptation, observers judged the duration of a brief (600 ms) upwards-moving (3° s−1), 100% coherence test pattern at the same location as the adapting pattern. Perceived duration of the test pattern was estimated by having observers judge whether a comparison pattern (100% coherence) of variable duration, centred 5° right of fixation and moving in the opposite direction to the test pattern, was of longer or shorter duration than the 600 ms test pattern.Figure 1.


Perceived duration of brief visual events is mediated by timing mechanisms at the global stages of visual processing
(a) Experimental timeline. (b) Change in perceived duration as a function of the adaptor coherence level. Negative and positive values indicate duration compression and duration expansion, respectively. It is clear that increasing the adaptor's motion coherence level leads to a concomitant increase in the magnitude of the duration compression effect (error bars are ±1 s.e.).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383839&req=5

RSOS160928F1: (a) Experimental timeline. (b) Change in perceived duration as a function of the adaptor coherence level. Negative and positive values indicate duration compression and duration expansion, respectively. It is clear that increasing the adaptor's motion coherence level leads to a concomitant increase in the magnitude of the duration compression effect (error bars are ±1 s.e.).
Mentions: Observers adapted for 30 s to a moving random dot pattern centred 5° left of a central fixation point, in which each dot moved at the same speed 3° s−1 (figure 1a). Observers maintained fixation throughout each block of trials. Within each block of trials the adaptor pattern was assigned a fixed motion coherence value of 0%, 20%, 40%, 60%, 80% or 100%. The lifetime of each dot was set to the duration of the adaptor stimulus. In the case of 100% motion coherence all dots in the adaptor stimulus drifted upwards; for lower motion coherence levels the probability that a dot was assigned the signal motion direction (upwards) on each frame was determined by the motion coherence parameter. Thus, for the 20% motion coherence condition each dot had a 0.2 probability of being assigned the signal motion direction, and a 0.8 probability of being assigned a random motion direction, on a given frame. Using the terminology of Scase et al. [24], who looked at motion thresholds for a variety of different types of RDK, our random dot pattern is classified as random walk using the different rule. After 30 s adaptation, observers judged the duration of a brief (600 ms) upwards-moving (3° s−1), 100% coherence test pattern at the same location as the adapting pattern. Perceived duration of the test pattern was estimated by having observers judge whether a comparison pattern (100% coherence) of variable duration, centred 5° right of fixation and moving in the opposite direction to the test pattern, was of longer or shorter duration than the 600 ms test pattern.Figure 1.

View Article: PubMed Central - PubMed

ABSTRACT

There is a growing body of evidence pointing to the existence of modality-specific timing mechanisms for encoding sub-second durations. For example, the duration compression effect describes how prior adaptation to a dynamic visual stimulus results in participants underestimating the duration of a sub-second test stimulus when it is presented at the adapted location. There is substantial evidence for the existence of both cortical and pre-cortical visual timing mechanisms; however, little is known about where in the processing hierarchy the cortical mechanisms are likely to be located. We carried out a series of experiments to determine whether or not timing mechanisms are to be found at the global processing level. We had participants adapt to random dot patterns that varied in their motion coherence, thus allowing us to probe the visual system at the level of motion integration. Our first experiment revealed a positive linear relationship between the motion coherence level of the adaptor stimulus and duration compression magnitude. However, increasing the motion coherence level in a stimulus also results in an increase in global speed. To test whether duration compression effects were driven by global speed or global motion, we repeated the experiment, but kept global speed fixed while varying motion coherence levels. The duration compression persisted, but the linear relationship with motion coherence was absent, suggesting that the effect was driven by adapting global speed mechanisms. Our results support previous claims that visual timing mechanisms persist at the level of global processing.

No MeSH data available.