Abstract
In a reaction-time task, an increase in stimulus uncertainty led to increased RT. This was achieved by varying the number of possible sensory modalities for the signal, changing the length or variability of a warning foreperiod, and concurrently presenting masking noise. At the highest levels of uncertainty, concurrently-monitored pupillary dilation showed an overall flattening of associated response peaks, together with a rise in baseline levels. There was also evidence of expectancy phenomena with nonoccurring, anticipated signals.
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Bradshaw, J.L. Pupillary changes and reaction time with varied stimulus uncertainty. Psychon Sci 13, 69–70 (1968). https://doi.org/10.3758/BF03342414
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DOI: https://doi.org/10.3758/BF03342414