Abstract
Fixations provide natural and unique time-locking events in the electroencephalographic (EEG) record enabling the measurement of fixation-related potentials (FRPs). The most prominent FRP component is commonly referred to as the lambda response, a positive deflection over occipital electrodes peaking 80-100 ms post fixation, reflecting afferent input to visual cortex. Prior work suggests the lambda response may be a useful index of visual information processing; however, there are considerable gaps in our understanding of this response that need to be addressed before this can be realized. While it is know that the lambda potential is responsive to feature-based manipulations and the size of the preceding saccade, prior research has not adequately controlled for these manipulations in free viewing paradigms, nor has the potential interaction of these effects been investigated. The current experiment addresses these concerns by systematically manipulating spatial frequency in a free view task requiring a range of saccade sizes. Importantly, when estimating the FRPs we evaluate how removing independent components (IC), associated ocular motion artifacts, affects lambda response amplitude. Our results indicate that removing these ocular ICs did not significantly affect the amplitude of this occipital potential. Moreover, the results showed that spatial frequency and saccade magnitude each produce significant effects on lambda amplitude, where amplitude decreased with increasing spatial frequency and increased as a function of saccade size. The amplitude differences between spatial frequencies were maintained across all saccade magnitudes suggesting these effects are produced from distinctly different and uncorrelated sources.
Meeting abstract presented at VSS 2018