Motion-Induced Blindness Using Increments and Decrements of Luminance

Motion-induced blindness describes the disappearance of stationary elements of a scene when other, perhaps non-overlapping, elements of the scene are in motion. We measured the effects of increment (200.0 cd/m2) and decrement targets (15.0 cd/m2) and masks presented on a grey background (108.0 cd/m2), tapping into putative ON- and OFF-channels, on the rate of target disappearance psychophysically. We presented two-frame motion, which has coherent motion energy, and dynamic Glass patterns and dynamic anti-Glass patterns, which do not have coherent motion energy. Using the method of constant stimuli, participants viewed stimuli of varying durations (3.1 s, 4.6 s, 7.0 s, 11 s, or 16 s) in a given trial and then indicated whether or not the targets vanished during that trial. Psychometric function midpoints were used to define absolute threshold mask duration for the disappearance of the target. 95% confidence intervals for threshold disappearance times were estimated using a bootstrap technique for each of the participants across two experiments. Decrement masks were more effective than increment masks with increment targets. Increment targets were easier to mask than decrement targets. Distinct mask pattern types had no effect, suggesting that perceived coherence contributes to the effectiveness of the mask. The ON/OFF dichotomy clearly carries its influence to the level of perceived motion coherence. Further, the asymmetry in the effects of increment and decrement masks on increment and decrement targets might lead one to speculate that they reflect the ‘importance’ of detecting decrements in the environment.

A closer look at four-dot masking of a foveated target

Four-dot masking with a common onset mask was recently demonstrated in a fully attended and foveated target (Filmer, Mattingley & Dux, 2015). Here, we replicate and extend this finding by directly comparing a four-dot mask with an annulus mask while probing masking as a function of mask duration, and target-mask separation. Our results suggest that while an annulus mask operates via spatially local contour interactions, a four-dot mask operates through spatially global mechanisms. We also measure how the visual system’s representation of an oriented bar is impacted by a four-dot mask, and find that masking here does not degrade the precision of perceived targets, but instead appears to be driven exclusively by rendering the target completely invisible.

Dynamic Contrast Perception Assessed by Pattern Masking

The perceived contrast of a pulsed grating of about 100 ms duration can exceed that of shorter or longer exposures. We investigated this contrast enhancement effect with pattern masking. The pulsed mask patterns were extended cosines (5 deg square, 35 cd m−2 mean luminance, 0.3 contrast) of 50 to 500 ms duration. Mask spatial frequency was 1 or 6 cycles deg−1. The test patterns (of equivalent spatial frequency) were sixth derivative Gaussians, either positive (ON pathway mediation) or negative (OFF pathway mediation) and of 30 ms duration. The test pattern could be centred on a light bar of the cosine (positive contrast) or a dark bar (negative contrast). Test and mask had simultaneous onset. For a 1 cycle deg−1 test and mask of the same polarity, the test threshold/mask duration function is nonmonotonic (peak at 83 – 100 ms). The function was similar for either positive or negative stimuli. Thus, we measured an analogue to the contrast enhancement effect, and found enhancement for negative as well as positive contrast components. For same-polarity 6 cycles deg−1 test and mask, threshold increased monotonically to 500 ms (no enhancement). For both 1 and 6 cycles deg−1 stimuli of opposite polarity, the threshold/mask duration function is sharply elevated and constant for masks of 83 ms or more. The same-polarity masking functions imply activation of either transient (1 cycle deg−1 stimuli) or sustained (6 cycles deg−1 stimuli) ON or OFF pathways. The opposite-polarity functions suggest that the time course of ON — OFF pathway interaction is similar for sustained and transient pathways.