The Effect of Visual Task Difficulty on the Fixation-Related Lambda Response
Technical Report,01 Aug 2015,30 Sep 2016
US Army Research Laboratory Aberdeen Proving Ground United States
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Fixation-related potentials further our understanding of overt orienting by leveraging rather than limiting eye movements in experimental paradigms. The lambda response, a prominent neural signature of the fixation-related potential, has been used to examine stimulus-driven and cognitive influences on early stages of visual processing and overt orienting behavior. Prior experiments have shown changes in lambda response amplitude due to top-down effects from auditory task difficulty however, it is still not clear to what degree this component is sensitive to changes in visual task difficulty. Here we modulated difficulty using 2 different visual tasks. In the first, difficulty was manipulated via the working memory load of a visual N-Back task while eye movements were systematically guided across a search grid. For the second task we used a modified Tetris game where difficulty was manipulated via tetrad fall speed, without imposing eye movement constraints. Subjective reports, behavior, and other physiological measures confirmed our task manipulations increased difficulty in both paradigms. The results showed that lambda response amplitude was significantly attenuated at high with respect to low difficulty levels in the N-Back task. In contrast, the Tetris task exhibited the opposite effect showing increased lambda amplitude as a function of task difficulty. Critically, these effects were maintained when correcting for overlapping neural activity elicited from temporally adjacent stimuli and saccadic events. Together, our results suggest that task difficulty may differentially affect early visual processing depending on the requisite cognitive and perceptual processes. Understanding how the lambda response is affected by task difficulty in the visual domain may provide a more direct way to index task demands in search behavior without relying on a secondary task or probe stimulus.
- Anatomy and Physiology