Gaze capture by eye-of-origin singletons: interdependence with awareness.

Where we look in visual tasks is determined by both bottom-up and top-down factors. One theory (Li, 1999a, 2002) suggests that visual area V1 creates a bottom-up saliency map, guiding gaze through extensive projections to the superior colliculus. V1 is the only visual cortical area that represents the eye of origin of an input and is also least associated with awareness; I therefore predicted that an ocular singleton (i.e., an item only shown to one eye among other items shown to the other eye) that is perceptually indistinct might nevertheless attract gaze. In visual searches for an orientation singleton target bar among uniformly oriented background bars, an ocular singleton non-target bar, at the same eccentricity as the target from the center of the search display, often captured the first search saccade. The chance of this capture was above 50% (e.g., 75%) when the eccentricity of the singletons was large and luminance did not vary between the bars, and it was below 50% when the eccentricity was smaller and luminance varied. After each search trial, observers reported whether an ocular singleton non-target (which was actually presented in half of the trials) had been shown. When different bars had similar luminance, misses numbered less than 50% and were independent of whether the gaze was captured by the ocular singleton. However, when luminance varied sufficiently between the bars, 50% were missed overall, albeit significantly less for those that captured gaze. The experiments in this work followed the guidelines in the Declaration of Helsinki.