Abstract
Observers are often unaware of changes made to the visual environment when attention is not focused at the location of the change. This phenomenon, known as change blindness, has been extensively studied using psychophysics and fMRI. Yet its correlates at the single cell level remain unclear. We recorded from the medial temporal lobe (MTL) of patients with pharmacologically intractable epilepsy, implanted with depth electrodes and microwires, to localize the focus of seizure onsets. Subjects were shown one set of 4 simultaneously presented images twice, each time for 1s, with a brief blank interval of 1.5s between the 2 presentations. On half the trials, a change occurred at one of the four locations, and subjects had to report whether they detected the change or not. In separate “screening” sessions, specific images that cells were visually responsive to (“preferred stimuli”) were determined. We investigated neuronal responses when the set of preferred stimuli were used as changing elements. We have currently recorded from 29 visually responsive cells in 10 patients using this paradigm. Over these cells, the preferred stimuli elicited significantly higher firing rates on correct trials (e.g. change detection) compared to incorrect (e.g. change blindness) trials. For each cell, we were able to predict on a trial-by-trial basis (using an ROC analysis) whether or not a change occurred 65% of the time on average. Thus, the firing rates of certain MTL cells constitute a neural correlate of change detection and change blindness.