Introduction: It has been shown that subjects are faster and more accurate at detecting or discriminating stimuli when they are more certain of where a stimulus will appear. We have shown that a probability paradigm, in which observers use the probability of where a stimulus is likely to occur, can direct the allocation of resources and improve accuracy with increasing probability, or spatial certainty (Ciaramitaro et al, 2001). We now study the temporal dynamics of attention across probability transitions, to investigate how quickly observers track shifts in probability, as the certainty of where to attend changes. Method: Six observers performed an orientation discrimination task, viewing an extrafoveal stimulus (102ms) that was followed by a mask (102ms) after a delay of 17, 35 or 52ms. The probability of stimulus occurrence in the left or right hemifield switched between 20% and 80% in several blocks of ∼200 trials each. Behavioral data were convolved with a gaussian to derive a trial-by-trial running estimate of fluctuations in performance over time. Results & Conclusion: When probability transitions were signaled, observers' overall performance improved as probability increased across blocks, whereas when transitions were not signaled, and observers may have been less certain of the probability condition, their overall performance was not well matched to changes in probability. On a trial-by-trial basis, performance within a block was not always stable, potentially obscuring overall differences between blocks, and performance changes across blocks often showed rapid transitions, suggesting that observers learned the new probability quickly. Quantifying the dynamics of changes in behavior over time is an important step if we ultimately want to link such changes to dynamic changes at the neuronal level as we switch attention to different locations.
ASJC Scopus subject areas
- Sensory Systems