Abstract
Studies investigating the neural mechanisms of time perception often measure brain activity while participants perform a temporal task. However, several of these studies are based exclusively on tasks in which time is relevant, making it hard to dissociate activity related to decisions about time from other task-related patterns. In the present study, human participants performed a temporal or color discrimination task of visual stimuli. Participants were informed which magnitude they would have to judge before or after presenting the two stimuli (S1 and S2) in different blocks. Our behavioral results showed, as expected, that performance was better when participants knew beforehand which magnitude they would judge. Electrophysiological data (EEG) was analysed using Linear Discriminant Contrasts (LDC) and a Representational Similarity Analysis (RSA) approach to investigate whether and when information about time and color was encoded. During the presentation of S1, we did not find consistent differences in EEG activity as a function of the task. On the other hand, during S2, we found that temporal and color information was encoded in a task-relevant manner. Taken together, our results suggest that task goals strongly modulate decision-related information in EEG activity.
Highlights
Perceptual timing is essential for humans and other animals to interact with their environments
There was no difference in bias, measured by the Point of Subjective Equality between mixed and pure blocks (PSETimePure = 0.947 ± 0.025, PSETimeMixed = 0.981 ± 0.032, t(20) = −1.480, p = 0.154, d = 0.323, BF10 = 0.585; PSEColorPure = 1.023 ± 0.021, PSEColorMixed = 0.999 ± 0.023, t(20) = 0.986, p = 0.336, d = 0.215, BF10 = 0.350)
Time and color-related activity: In a second analysis, we investigated if the duration or color of S1 modulated Electrophysiological data (EEG) activity
Summary
Perceptual timing is essential for humans and other animals to interact with their environments. A commonly used task to study this ability is temporal discrimination, in which participants have to judge whether a given duration is shorter or longer than a reference. Several studies have compared temporal discrimination tasks with discrimination of other attributes, such as color [1,2], size [3], space [4] and numerosity [5]. Coull and colleagues [1], using functional Magnetic Resonance Imaging, found a higher activation of areas such as the pre-SMA and a network of other cortical and striatal areas when participants paid more attention to the duration than the color of a stimulus. Studies involving color discrimination as a contrast task change color dynamically to make the tasks more cognitively comparable.
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