Effects of imagery on vernier acuity under conditions of induced depth.

Imagery interferes with visual acuity (the "Perky effect") when an image is close to a visual target and both the image and the acuity target are located in the same depth plane. Whether imagery-induced interference occurs when a mental image and a target are separated by induced depth was investigated. Participants projected an image in front of or behind a vernier acuity target on a frontal or back plane suggested by the panels of an outline cube. A drop in accuracy for the target was found when an image was projected in front of, but not behind, the target. Thus, induced depth can influence the Perky effect. By contrast, real lines interfered with the target regardless of perceived depth plane, which is inconsistent with the hypothesis that imagery and perception are equivalent. Results support the hypothesis that images interfere with perception only when the participant must see through an image to obtain information specifying the visual target. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Illusory" illusory conjunctions: The conjoining of features of visual and imagined stimuli.

The question of whether illusory conjunctions would occur with visual mental imagery was investigated. In 4 experiments, participants were tachistoscopically presented displays of geometrical figures (varying in shape, color, and solidity) flanked by 2 digits. For half of the trials, participants imagined one of the figures in the display. Illusory conjunctions occurred between the features of the physical (cued) and imagined figures, which suggests that imagery influences perception at the level of visual processing at which features are combined. Moreover, the conjunction errors induced by an imagined figure were similar to those induced by a physical figure with the same features. The pattern of errors could not be accounted for by guessing. Together, these findings support the view that there can be correspondence between visual imagery and visual perception. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

How visual imagery interferes with vision.

Mental visual imagery interferes with vision: the Perky (1910) effect. Is the effect optical, sensory, perceptual, attentional, or just a response bias? Acuity was measured (in undergraduates and graduates) using target lines, with and without images (of lines). Optics (fixation, pupil size, accommodation), response bias, global attention (effort, diversion of attention to imagery), perceptual assimilation (target incorporation by imagery) and perceptual masking (of target by imagery) all fail to explain the effect. Foveally, local attention plays a limited role, as the Perky effect in divided attention is half that in focused attention, but this interaction vanishes with extrafoveal targets. Images produce primarily sensory interference, mimicking a reduction in target energy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)