Further explorations of 'perceptual scotomas'
Here are some demonstrations of the various phenomena and manipulations discussed in the following paper:
New, J. J., & Scholl, B. J. (under review). Motion-induced blindness for dynamic events: Further explorations of the 'perceptual scotoma' hypothesis.These demonstrations are provided as both Flash (.swf) and MP4 animations, which can be downloaded or viewed directly in many web-browsers. These movies are a bit large and choppy, but they should be sufficient to illustrate the basic manipulations. If you have any trouble viewing the movies, downloading them and then playing them from your local hard-drive may help. As highly compressed versions of the original stimuli constructed for demonstration purposes, these movies may not preserve the precise spatial and temporal characteristics of the originals. The .swf versions should automatically loop, and the files are quite small; the .mp4 files will need to be downloaded and manually looped in order to play effectively, but they may be more compatible with a greater variety of modern platforms.
Motion-induced blindness (MIB) is a striking phenomenon in which fully visible and attended objects will repeatedly fluctuate into and out of conscious awareness when superimposed onto certain global moving patterns. Whereas previous accounts have explained MIB by appeal to a limitation or failure of visual perception, we proposed the perceptual scotoma hypothesis (New & Scholl, 2008, Psychological Science) which interprets MIB as a functional inference in visual processing -- eliminating some stimuli from awareness in much the same way that the visual system identifies and compensates for some visual impairments. Here we report several new features of MIB that were motivated by the perceptual scotoma account, and that each involve aspects of MIB for dynamic targets.
Demonstration #1: The Basic MIB Display (.swf, .mp4)
One of the most striking experimental manipulations of visual awareness is that of motion-induced blindness (MIB), wherein salient objects in full view can repeatedly fluctuate into and out of conscious awareness when superimposed onto certain global moving patterns. Here is a basic example: Fixate the concentric white circles and attend to the moving blue crosses, and then notice what happens to the otherwise-salient yellow disc. This display is similar to previous MIB experiments.
Demonstration #2: Multitarget Retinal Stability (.swf, .mp4)
Observers visually tracked the slowly translating fixation circles while peripherally attending to the two target discs that were also moving in the upper left region of the display. MIB was stronger for the target that moved in step with fixation compared to the target that moves in the opposite direction as fixation. Because most types of visual injuries are retinally stable, an anomalous target may be judged as less likely to be in the outside world if it is moving with fixation vs. relative to fixation.
Demonstration #3a: Luminance Distortion (.swf, .mp4)
Demonstration #3b: Contraction Distortion (.swf, .mp4)
Demonstration #3c: Expansion Distortion (.swf, .mp4)
Demonstration #3d: Curvature Distortion (.swf, .mp4)
Demonstration #3e: Color Distortion (.swf, .mp4)
Observers fixated the central fixation point and peripherally attended to a target defined by the persistent distortion of mask elements passing through a small region in the upper left quadrant of the display. Such manipulations are similar to local visual disturbances resulting from scotomas that are not entirely opaque and thus only attenuate or distort stimuli within affected regions (such as metamorphopsias). These 'active' targets all disappeared due to MIB.
Demonstration #4: Drifting Up vs. Down (.swf, .mp4)
Observers fixated the central fixation-point circles while peripherally attending the slowing moving yellow disc. MIB was stronger when the target drifted slowly downward compared to upward -- perhaps because of the related motions of floaters in the eye's vitreous humor. The paper reports additional control experiments that rule out alternate explanations based on eccentricity.