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Eric Taylor, Minal Patel, Jay Pratt; Hand proximity biases overt – not covert – orienting. Journal of Vision 2016;16(12):1276. doi: https://doi.org/10.1167/16.12.1276.
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The various effects of altered vision near the hands are sometimes hard to reconcile. For example, the first two major investigations in this literature reported near-hand attentional prioritization and no interaction with peripheral cues (Reed, Grubb, & Steele, 2006) and prolonged attentional disengagement and interactions with peripheral cues (Abrams, Davoli, Du, Knapp, & Paull, 2008). Noting these and other discrepancies, the modulated visual pathways (MVP) theory proposed an alternate account, whereby hand proximity up-regulates magnocellular processing via the dorsal stream. This theory posits an alternative explanation for earlier reports of attentional prioritization (faster detection RTs) for peripheral targets in near-hand space: Eye movements should be faster toward stimuli appearing in near-hand space due to an enhanced collicular response. We conducted two experiments to investigate this alternative account. First, we conducted a close replication of Reed et al.'s (2006) spatial cueing task using eye-tracking and a strict gaze-contingent window at fixation, forcing covert rather than overt orienting. When eye movements were expressly forbidden, we failed to replicate the faster detection for stimuli in near-hand space, suggesting that earlier reports were caused by biases in eye movements or starting eye position. Second, we put MVP to the test in a fixation-offset gap effect paradigm. Participants made speeded eye movements to peripheral onsets either with or without a fixation stimulus. The presence of a fixation stimulus inhibits the activity of burst neurons in the superior colliculus, slowing eye movements. According to MVP, hand proximity should up-regulate the collicular signal, reducing saccadic RTs in the presence of a fixation stimulus. Consistent with this expectation, we observed faster saccadic RTs with a fixation stimulus near versus far from the hand. This reduced gap effect is difficult to explain with an attentional account of altered vision near the hands.
Meeting abstract presented at VSS 2016
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