Figure 3.

Effect of microstimulation on psychophysical thresholds in two monkeys performing the spatial attention task. (a) Comparison of the distribution of luminance change thresholds obtained with and without stimulation when the attention task was performed inside of the MF. The vast majority of threshold points fall below the line of unity, illustrating the tendency of thresholds to be lower with stimulation. (b) Average decrease in psychophysical thresholds obtained when the attention task was performed inside or outside the MF in each monkey. The reduction in threshold signifies the difference in target luminance change required for equal performance on stimulation and control trials, expressed as a percentage of the control contrast threshold [(1 − [contrast_stim./contrast_control]) × 100]. Positive values denote decreases in threshold with stimulation, whereas negative values denote increases. Targets positioned outside of the MF were on average 17° from the MF, but within the same hemifield. Double asterisks (**) denote a significance of P < 0.001.