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Paolo Martini; Two memory components explain sequential dependencies in a search task. Journal of Vision 2008;8(6):1167. doi: 10.1167/8.6.1167.
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© ARVO (1962-2015); The Authors (2016-present)
PURPOSE. To identify the characteristics of memory processes responsible for sequential dependencies in the Priming of Pop Out (PoP) paradigm.
METHODS. Stimuli were 3 bright and dark grayscale diamonds with a notch on the left or right side, displayed on a uniform gray background. Observers identified the odd target (dark/bright among bright/dark distracters) and responded by indicating the side of the notch. Color and notch were chosen randomly and independently on each trial. Reaction times were collected from individual observers running in blocks of 500 trials, totaling more than 10000 trials per observer.
RESULTS. Reaction times from each block of trials were de-trended with a 2nd order polynomial and z-scored. Lag 1–40 cross-correlations between the color/response series and the reaction time series were calculated to obtain 1st order Wiener kernels identifying the memory for color/response. The kernels were then averaged across blocks. For both color and response, kernels were well described by the sum of 2 exponentials comprising a fast and a slow component. The fast component is limited to 1 trial back and can be facilitatory or inhibitory. The slow component relaxes completely in about 20 trials and is always facilitatory. Calculation of second-order cross-kernels between color and response revealed a remarkable linearity, indicating independence of memory for color and response.
CONCLUSION: Memory in PoP is comprised of 2 components: a fast, explicit, one-trial-back component that can be facilitatory or inhibitory and varies considerably in gain across observers; a second, implicit, slow component that is always facilitatory and less variable across observers. Memories for color and response are independent and as such do not support the hypothesis of episodic representation in PoP. There are strong similarities in form with the kernels obtained with reward tasks in monkey, suggesting the possibility of common mechanisms for attention and reward processing.
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