Majority of studies in time perception uses visual objects like faces (emotional, non-emotional), geometrical figures, scenes, numbers, etc as stimuli. Although these complex images have been shown to influence time perception (addressing different questions), but the role of basic perceptual features (like contrast) which constitutes these complex images are rarely studied. A recent study by Christopher Benton and Annabelle Redfern published in Frontiers in Psychology, investigated the role of contrast on perceived duration.
They based their hypothesis on two lines of research, first are the adaptation studies which shows duration compression explained by adaptation-related stimulus-specific reduction in neural activity in early visual areas. And second are those studies which shows increase in neural activity in early visual areas with increase in contrast. So from these studies they hypothesized that, if adaptation related decrease in neural activity in early visual areas is linked to decrease in perceived duration then contrast based increase in neural activity in early visual areas should lead to increase in perceived duration.
To test this hypothesis they used dynamic spatial noise patterns as stimuli with three levels of contrast (0.1, 0.3, and 0.9). Each noise element in this pattern changed its luminance sinusoidally at temporal frequency of 4Hz. Two types of spatial filters i.e. circular Gaussian envelope or circular aperture, were used to generate stimuli patches with either gradient boundary or sharp boundary. The sharp boundary circular patch acted as size control stimuli, as in gradient boundary the perceived size might also change with contrast confounding the timing results.
To measure the effect of contrast on perceived duration they used adaptive match-to-standard procedure. In each trial participants saw a standard stimuli (with contrast 0.3) for 600 ms followed by a match (test) stimuli (with either 0.1 or 0.9 contrast) displayed for time randomly decided by the adaptive procedure between 125ms to 3000ms. Participants reported which of the two appeared for longer duration. Gradient boundary and sharp boundary stimuli were used in separate blocks. Results indicated that participants perceived the high contrast stimuli to be longer in duration compared to low contrast stimuli irrespective of its boundary type.
Based on previous study linking contrast with temporal frequency, one might argue that the above results could not be due to contrast influencing duration but rather due to contrast influencing temporal frequency and which in-turn influencing duration. To control this they performed another experiment in which they first found the temporal frequency threshold for low and high contrast for individual participants. And then used individual specific temporal frequency to test the effect of contrast on perceived duration. In this experiment, even after controlling for temporal frequency change, results showed that perceived duration increased with contrast.
Authors suspected that the above increase in perceived duration due to contrast may not reflect entirely due to sustained neural activity but can also be explained by assuming some fixed neural activity threshold for stimulus onset and offset detection. In such a scenario, the perceived duration changes due to contrast is a result of difference in onset and offset timing rather than contrast driven sustained activity in the early visual areas. To investigate this, they designed a third experiment using a method of constant stimuli and tested the effect of contrast (0.1 and 0.9) on onset and offset perception. They found that contrast does influence the onset and offset perception of stimulus but this could account for around 20ms of difference between high and low contrast stimuli, which still cannot fully explain the 60ms difference they got in both the previous experiments.
Overall, the above study demonstrated the influence of low level perceptual feature such as contrast on perceived duration, further studies with multiple standard duration and larger N is needed to fully understand the role of contrast in time perception . As pointed by authors, despite 89% reduction in contrast it only led to just 10% reduction in perceived duration, raises further interesting questions about the mechanisms underlying such effects.
In my opinion, more studies are needed with not only contrast but also with other low level perceptual features like spatial frequencies, luminance; and also with curvatures, and textures, leading to complex images like faces. So that we can understand the role of specific components in altering time perception, which in future would enable researchers to model and predict (only to certain extend as complex objects influences are based on associated meaning as well) the perceived time of a complex image just by analyzing the lower level components of an image.
Source article: Benton, C. P., & Redfern, A. S. (2016). Perceived Duration Increases with Contrast, but Only a Little. Frontiers in Psychology, 7.
—-Mukesh Makwana, Doctoral student, (mukesh@cbcs.ac.in)
Centre of Behavioural and Cognitive Sciences (CBCS), University of Allahabad, India.
