Luminance and color are strong and self-sufficient cues to pictorial depth in visual scenes and images. The present study investigates the conditions Under which luminance or color either strengthens or overrides geometric depth cues. We investigated how luminance contrasts associated with color contrast interact with relative height in the visual field, partial occlusion, and interposition in determining the probability that a given figure is perceived as ‘‘nearer’’ than another. Latencies of ‘‘near’’ responses were analyzed to test for effects of attentional (...) selection. Figures in a pair were supported by luminance contrast or isoluminant color contrast and combined with one of the three geometric cues. The results of Experiment 1 show that luminance contrasts associated with hue, when it does not interact with other hues, produces the same effects as achromatic luminance contrasts: The probability of‘‘near’’ increases with luminance contrast while the latencies for ‘‘near’’ responses decrease. Partial occlusion is found to be a strong enough pictorial cue to support a weaker red luminance contrast. Interposition cues lose out against cues of spatial position and partial occlusion. The results of Experiment 2, with isoluminant displays of varying color contrast, reveal that red color contrast on a light background supported by any of the three geometric cues wins over green or white supported by any of the three geometric cues. On a dark background, red color contrast supported by the interposition cue loses out against green or white color contrast supported by partial occlusion. These findings reveal that color is not an independent depth cue, but is strongly influenced by luminance contrast and stimulus geometry. Systematically shorter response latencies for stronger ‘‘near’’ percepts demonstrate that selective visual attention reliably detects the most likely depth cue combination in a given configuration. (shrink)

The distinction between bottom-up and top-down control of action has been central in cognitive psychology, and, subsequently, in functional neuroimaging. While the model has proven successful in describing central mechanisms in cognitive experiments, it has serious shortcomings in explaining how top-down control is established. In particular, questions as to what is at the top in top-down control lead us to a controlling homunculus located in a mythical brain region with outputs and no inputs. Based on a discussion of recent brain (...) imaging experiments, we argue for the need to factor the interaction between the experimenter and the experimental participant into a realistic understanding of top-down control. We suggest these interactions involve a ‘sharing of scripts’ for perception and action that may be described as ‘top-top processes.’ We thereby expand the understanding of the homunculus to include elements of social cognition. This conceptual reconfiguration may grant some sort of asylum for a—not very omnipotent—homunculus. (shrink)