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Abstract:
Humans monitor environmental regularities to construct internal models. For detecting the emergence of regular auditory sequences consisting of 5, 10, or 20 rapid tone pips (each lasting 50 ms), research suggests that humans require, on average, only one and a half repetitions of a sequence, and their performance is on par with an ideal observer model. We investigated whether this result transfers to the visual domain by assessing the number of repetitions required to detect regular visual sequences. We presented participants (N=11) with sequences of white dots, each lasting 50 ms and appearing within a grid of 20 slots which was either 1-dimensional or 2-dimensional. The sequences involved transitions from random to regular patterns. Random patterns involved uniformly sampled positions in the grid, whereas regular patterns consisted of either 5, 10, or 20 randomly-chosen positions that were repeated over time. We instructed participants to report transitions from random to regular patterns and measured their pupil size to assess task-evoked pupil dilation responses, previously associated with the detection of auditory regularities. We found that detecting visual regularities required at least two and a half repetitions, and the number of repetitions needed increased with sequence length. Detecting visual regularities was easier in a 2-dimensional grid as opposed to a 1-dimensional grid, but the detection process induced pupil dilation responses in both cases.
