Abstract
Previous research has documented that contour detection and integration may either be affected by local features such as the distances between elements or by high-level cognitive factors such as attention in our visual system. Less is known about how low and high level factors interact to influence contour integration. In this paper, we investigated how attention modulates contour integration through saliency (different element spacing) and topological propert ies (circle or S-shaped) when the state of conscious awareness is manipulated. A modified inattentional blindness (IB) combined with the Posner cuing paradigm was adopted in our three-phased experiment (unconscious-training-conscious). Attention was manipulated with high or low perceptual load for a foveal go/no-go task. Cuing effects were utilized to assess the covert processing of contours prior to a peripheral orientation discrimination task. We found that (1) salient circles and S-contours induced different cuing effects under low perceptual load but not with high load; (2) no consistent pattern of cuing effects was found for non-salient contours in all the conditions; (3) a positive cuing effect was observed for salient circles either consciously or unconsciously while a negative cuing effect occurred for salient S-contours only consciously. These results suggest that conscious awareness plays a pivotal role in coordinating a closure effect with the level of perceptual load. Only salient circles can be successfully integrated in an unconscious state under low perceptual load although both salient circles and S-contours can be done consciously. Our findings support a bi-directional mechanism that low-level sensory features interact with high-level cognitive factors in contour integration.
Highlights
Contour detection and integration are crucial for the visual system to generate a coherent representation of visual objects, especially in complex environments
We reasoned that the presence of irrelevant contours in a cued or uncued visual field might involuntarily interfere with the subsequent behavioral performance of a primary task (Gabor orientation discrimination), and a different level of detectability of contours could lead to differential Posner cuing effects (Li & Li, 2015; Zhang et al, 2012)
This study demonstrated how the perceptual load interacted with saliency and topological properties in affecting contour integration with or without conscious awareness
Summary
Contour detection and integration are crucial for the visual system to generate a coherent representation of visual objects, especially in complex environments. Visual contour integration is assumed to vary with low-level features such as color (Mcilhagga & Mullen, 1996; Mullen, Beaudot & Mcilhagga, 2000), orientation (Nelson & Frost, 1985), spatial frequency (Field, Hayes & Hess, 1993), saliency (Li & Gilbert, 2002), and topology (Kovács & Julesz, 1993). Contour integration generally declines with increasing spaces between neighboring elements (Field, Hayes & Hess, 1993; Strother & Alferov, 2014). Global contour saliency is based on the local integration mechanisms of intermediate spatial extent (Li & Gilbert, 2002). It is widely accepted that proximity and continuation can be implemented physiologically through long-range horizontal connections in the primary visual cortex (V1) (Gilbert & Li, 2013; Hess, Hayes & Field, 2003; Li & Gilbert, 2002; Li, 1997)
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