Abrupt onsets in the visual field can change the appearance of subsequent stimuli, according to one interpretation, by engaging an attentional mechanism that increases effective stimulus contrast. However, abrupt onsets can also engage capacity-unlimited and thus attention-independent sensory mechanisms. We conducted a series of experiments to differentiate the sensory and attentional accounts. Observers compared the contrasts of uncued low-contrast peripheral targets with simultaneous targets cued by one of three cue types with different sensory attributes: white or black peripheral abrupt onsets and central gaze direction cues devoid of sensory activity near the target locations. Each cue facilitated the perception of perithreshold targets; however, the white abrupt onsets increased the perceived contrast of suprathreshold targets, whereas the black abrupt onsets tended to reduce the perceived contrast, and the gaze direction cues had no significant effect. The effectiveness of the gaze direction cues in automatically orienting attention was demonstrated in a control experiment in which they consistently speeded response times. The results suggest that sensory interaction, and not attention, is responsible for changes in appearance.

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The Fröhlich effect and flash-lag effect, in which moving objects appear advanced along their trajectories compared to their actual positions, have defied a simple and consistent explanation. Here, I show that these illusions can be understood as a natural consequence of temporal compression in the human visual system. Discrete sampling at some stage of sensory perception has long been considered, and if it were true, it would necessarily lead to these illusions of motion. I show that the discrete perception hypothesis, with a single free parameter, the perceptual moment or sampling rate, can quantitatively explain all of the scenarios of the Fröhlich and flash-lag effect. I interpret discrete perception as the implementation of data compression in the brain, and our conscious perception as the reconstruction of the compressed input.

Drawing on the empirical premise that attention makes objects look more intense (bigger, faster, higher in contrast), Ned Block has argued for mental paint, a phenomenal residue that cannot be reduced to what is perceived or represented. If sound, Block's argument would undermine direct realism and representationism, two widely held views about the nature of conscious perception. We argue that Block's argument fails because the empirical premise it is based upon is false. Attending to an object alters its salience, but not its perceived intensity. We also argue that salience should be equated with mental primer, a close cousin of mental paint that reintroduces difficulties for direct realism and representationism. The upshot is that direct realism and representationism are still in trouble, but not for the reason that Block thinks.