Image generation and processing of generated images in the cerebral hemispheres.

Recent computational models describing the contribution of the cerebral hemispheres to visual imagery have suggested an exclusive capacity of the left hemisphere to generate multipart images. A brief review of relevant findings indicates that the evidence presented in support of this suggestion is not entirely compelling; this prompted a reexamination of this issue in a lateral tachistoscopic study on normal adults. Sixteen subjects participated in two experiments in which they had to decide whether or not a lowercase letter contained a segment extending above or below the main body of the letter. This decision was made directly on lowercase letters in one experiment (perceptual task) and on their generated images in the other experiment (imagery task). The quality of the letters (clear or blurred) and the retinal eccentricity of stimulus presentation (small or large) were orthogonally manipulated. The perceptual task yielded no main effect of visual field but a significant interaction of visual field and letter quality. By contrast, the imagery task resulted in a left visual-field superiority but no interaction involving the visual fields—a departure from predictions based on current models of visual imagery. In addition, the pattern of results in the imagery task corresponded to that obtained with blurred letters in the perceptual task, suggesting limitations in spatial resolution of visual images. Implications of these results for models of cerebral lateralization and visual imagery are discussed. (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)     

Mental imagery and aging.

Young adult (aged 18–23 yrs) and elderly (aged 55–71 yrs) Ss performed 4 visual mental imagery tasks, each of which tapped different processes. The elderly had relatively impaired image rotation and image activation (the process of accessing and activating stored visual memories), and there was a hint that aging may impair the ability to maintain images. In contrast, the elderly were able to compose (the process of generating the segments of the shape, one by one) and scan visual mental images as well as young adults. However, when the authors correlated the mean performance of each age group across all the tasks, they found that the reaction times (RTs) of the elderly were almost perfectly predicted by the performance of the young Ss but that the error rates were not correlated. These findings suggest that although there is slowing with age, individual imagery processes are affected selectively by aging. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mechanisms of imagery-perception interaction.

A number of different research findings have shown that mental imagery can affect the perceptual processing of stimuli. The present research was aimed at characterizing the representations and processes underlying imagery–perception interactions. In 4 experiments, Ss mentally projected images of letters into the visual field, and either detected or detected and localized point threshold stimuli that fell on or off the image. Stimuli falling on the image were detected more often than stimuli falling off the image, consistent with the hypothesis that the representations at the interface between imagery and perception have an array format. When the facilitation was analyzed in terms of signal detection theory, it was found to consist only of criterion lowering, and not of enhanced sensitivity. The local criterion-lowering effect of imaged letters was then compared with the effect of perceiving a letter and attending to a letter. Perceiving a letter had no discernible effect on stimulus detection, whereas attending to the letter caused the same local criterion lowering, without sensitivity changes, as imaging the letter. This is consistent with the claims of U. Neisser (1976) and others that imagery is an attentional state. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attenuating verbal overshadowing through color retrieval cues.

Five experiments showed that interference resulting from verbalizing visual stimuli (verbal overshadowing) can be reduced by reintroducing visual cues present at encoding. Object color and background color were used as cues. Participants learned either easy- or hard-to-name figures and then performed an image rotation task. Before performing the imagery task, participants were re-presented with the color patch associated with each figure. Color re-presentation attenuated the impairment associated with easy-to-name stimuli (Experiment 1) as well as labeled hard-to-name stimuli (Experiment 2). However, background color cues had no effect on imagery performance (Experiment 3). Experiment 4 showed that naming the object colors at encoding makes color retrieval cues ineffective. Finally, Experiment 5 showed that object color cues can help participants to overcome previously exhibited impairment resulting from covert verbalization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Can mental images be ambiguous?

Argues that, although much recent research has emphasized the equivalence between imagery and perception, there are critical differences between these activities. Perception, initiated by an external stimulus, is to a large extent concerned with the interpretation of that stimulus; in contrast, images are created as symbols of something and hence need no interpretive process. Without a construal process, images do not allow reconstrual. In support of this argument, a series of 4 experiments with 65 university students was conducted to test whether Ss could reverse an ambiguous figure (e.g., duck/rabbit) in mental imagery. The S population contained many with vivid imagery, as assessed by a visual elaboration scale and the Vividness of Visual Imagery Questionnaire. In all 4 experiments, Ss were unable to reverse a mental image, but all Ss were able, immediately after this failure, to draw a picture from their mental image and then reconstrue the figure in their own drawing. This failure to reverse images occurs despite hints to the S, some coaching, and a moderate amount of training in figural reversal. Findings emphasize the difference between images and percepts. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual angle of the mind's eye before and after unilateral occipital lobectomy.

Do mental images occur in a spatially mapped (i.e., analog, or array-format) representational medium? S. M. Kosslyn's (1978) method was used to measure the visual angle of "the mind's eye" to estimate the extent of the imagery medium before and after unilateral occipital lobectomy. It was found that the overall size of the largest possible image was reduced following the surgery. In addition, only the horizontal extent, and not the vertical extent, of the imagery medium was reduced. Finally, it was determined that the S understood the tasks, was not aware of any predictions, and was unaffected by a strong demand characteristic in a different imagery task. These results are consistent with the hypothesis that imagery occurs in a spatially mapped representational medium dependent on occipital cortex. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Varieties of size-specific visual selection.

Compared time to evaluate stimuli of varying sizes. When Ss expect an upcoming stimulus to be a certain size, response time increases with the disparity between expected and actual size. There are, however, 2 size adjustment processes, and they reflect 2 types of visual selection. In the first, a shape-specific image representation is used to separate a visual object from a superimposed distractor. These representations require the type of slow size scaling demonstrated in imagery experiments. The second size scaling process is faster and not shape-specific. At any given time the visual system is set to process information at a particular scale, and that scale can be adjusted to match an object's size. Because both selection mechanisms depend on size, they probably occur at a relatively low, spatially organized processing level. These findings lead to a new explanation for results that had been taken as evidence for attentional selection at the level of object representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A developmental study of shape integration over space and time.

Three experiments, with 172 Ss (aged 6–24 yrs), examined the integration of shape information over successive glances. In Exps I and II, Ss classified line drawings subtending 1–26° visual angle as possible or impossible objects. Response times and errors increased as a function of figure size for all age groups. The decline in performance with figure size was greater for children than for adults. In Exp II, Ss also performed a classification task based on only 1 of the informative regions in each figure. Performance in the 2 tasks suggested that the ability to encode shape information from a single region of the figures did not change with age. In Exp III, a simultaneous condition, in which an intact figure was presented, was compared with sequential conditions in which blank intervals of 0–3 sec separated 2 views of different parts of the figure. All Ss classified the figures most quickly and accurately in the simultaneous condition, and children were more affected by longer delays between views than adults. It is concluded that these results point to age-related improvements in sequential integration of shape information, both when integration occurs through successive glimpses over space and when information is separated only in time. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differentiating visual and kinesthetic imagery in mental practice.

Through two experiments, the study sought to emphasize the usefulness of the visual and kinesthetic imagery in mental practice. In Experiment 1, it was hypothesized that when the task to be learned through mental practice necessitates the reproduction of a form by drawing, the visual image, which provides a wide span of apprehension, is more suitable than the kinesthetic image. On the other hand, the kinesthetic image that supplies inputs from the muscles' positions and movements should be more appropriate for the acquisition of the duration of the drawing. In Experiment 2, it was hypothesized that the task, transformed into a motor task necessitating minute coordination of the two hands, would benefit more from kinesthetic imagery. To have optimal control over what was actually experienced during mental practice, the participants' imagery skills were measured. The participants also benefited from prior imagery training. The results demonstrate that when using mental practice to initially acquire a task, visual imagery is better for tasks that emphasize form while kinesthetic imagery is better for those tasks that emphasize timing or minute coordination of the two hands. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Electrophysiological evidence for a shared representational medium for visual images and visual percepts.

Systematic effects of imagery on visual signal detection performance have been used to argue that imagery and the perceptual processing of stimuli interact at some common locus of activity (Farah, 1985). However, such a result is neutral with respect to the question of whether the interaction occurs during modality-specific visual processing of the stimulus. If imagery affects stimulus processing at early, modality-specific stages of stimulus representation, this implies that the shared stimulus representations are visual, whereas if imagery affects stimulus processing only at later, amodal stages of stimulus representation, this implies that imagery involves more abstract, postvisual stimulus representations. To distinguish between these 2 possibilities, we repeated the earlier imagery-perception interaction experiment while recording event-related potentials (ERPs) to stimuli from 16 scalp electrodes. By observing the time course and scalp distribution of the effect of imagery on the ERP to stimuli, we can put constraints on the locus of the shared representations for imagery and perception. An effect of imagery was seen within 200 ms following stimulus presentation, at the latency of the 1st negative component of the visual ERP, localized at the occipital and posterior temporal regions of the scalp, that is, directly over visual cortex. This finding supports the claim that mental images interact with percepts in the visual system proper and hence that mental images are themselves visual representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Monocular central-field occlusion for intractable diplopia

This report describes several methods of degrading imagery through the central portion of a spectacle lens to provide a cosmetically acceptable means of obtaining single vision in the central field of patients with intractable diplopia. For 2 strabismic patients with annoying diplopia, we applied to 1 spectacle lens a centrally placed disc (about 1 inch diameter) consisting of (1) translucent tap,a (2) a +7 D Fresnel lens,b or (3) stippled, clear lacquer. For 1 patient, the lacquer was the most acceptable; for the other, the tape was best. We present here the case reports for these 2 patients, showing why they preferred different image-degrading methods and how these and other methods of central-field image degrading can be advantageous even when diplopia is present across most of the visual field.     

A computational analysis of mental image generation: Evidence from functional dissociations in split-brain patients.

Recent efforts to build computer simulation models of mental imagery have suggested that imagery is not a unitary phenomenon. Rather, such efforts have led to a modular analysis of the image-generation process, with separate modules that can activate visual memories, inspect parts of imaged patterns, and arrange separate parts into a composite image. This idea was supported by the finding of functional dissociations between the kinds of imagery tasks that could be performed in the left and right cerebral hemispheres of 2 patients (a 19-yr-old male and a 32-yr-old female) who had previously undergone surgical transection of their corpus callosa. The left hemisphere in both Ss could inspect imaged patterns and could generate single and multipart images. In contrast, although the right hemisphere could inspect imaged patterns and could generate images of overall shape, it had difficulty in generating multipart images. Results suggest a deficit in the module that arranges parts into a composite. The observed pattern of deficits and abilities implied that this module is not used in language, visual perception, or drawing. Findings also suggest that the basis for this deficit is not a difficulty in simply remembering visual details or engaging in sequential processing. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overflow, first-sight, and vanishing point distances in visual imagery.

The relationship between the size of a familiar object and the distances at which it is imaged is examined in three experiments. The distance at which an imaged object overflows the visual field is linearly related to object size, a result consistent with the size–distance invariance hypothesis (Kosslyn, 1980). The distance at which an object is initially imaged, first-sight distance, is related to the object size by a power function with an exponent less than 1. In addition, time required to scan from the first-sight to the overflow distance increases as a function of the difference between the two distance estimates. The distance at which an imaged object becomes too small to be identified, vanishing point distance, is related to object size by a power function with an exponent less than 1. This result does not support predictions made from the size–distance invariance hypothesis or Kosslyn's model of visual imagery. Implications for a theory of visual imagery and memory are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Restoration of eidetic imagery via hypnotic age regression: A preliminary report.

Eidetic imagery involves the ability to examine a visual stimulus briefly, such as a picture or a design, and later project onto a neutral surface an image that represents an exact duplication of the original. This phenomenon is reliably found in a minority of children (8-20%), but is essentially nonexistent in adults. The present study used the differential frequency of eidetic imagery ability between children and adults as a basis for testing the validity or efficacy of hypnotic age regression. It was hypothesized that hypnotized adult Ss, given suggestions to regress to an earlier age, would revert to earlier modes of information processing, which for a small minority would include the ability to form eidetic images. Results indicate that 2 of the 20 undergraduate Ss achieved the criterion by identifying the correct figure in 3 10,000-dot stereograms while age regressed. None of the Ss correctly identified any stereogram figures while awake or merely hypnotized. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deciding how to act is not achieved by watching mental movies.

In the early days of research on visual imagery, it was believed that visual images are like pictures in one’s head. Only as the field matured did it come to be appreciated that visual images do not bear a first-order isomorphic relation to visual percepts. Now that the early days of research on motor imagery are coming to an end, it is important to ask whether motor images bear a first-order isomorphic relation to movements. We asked whether they do by focusing on internal simulations for motor planning. Our participants indicated which of two possible actions they preferred either by performing the preferred action or by indicating which action they would prefer to perform. We reasoned that if internal simulations of physical actions bear a first-order isomorphic relation to actual physical actions, the choices would be the same in the two conditions. They were not. We discuss the reasons for this outcome, including the adaptive advantage of a representational system for action which, like the representational system for vision, does not bear a first-order isomorphic relation to its external analog. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of luminance contrast on BOLD fMRI response in human primary visual areas

In this study, we examined the effect of stimulus luminance contrast on blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging within human visual cortex (V1 and extrastriate). Between experiments, the calibrated luminance of a single red LED covering 2 degrees of the subject's visual field was changed relative to a constant background luminance. This stimulus provided a different foveal luminance contrast for each experiment. We used an echo planar imaging sequence to collect blood-oxygenation-sensitive images during and in the absence of the presented stimulus. Our results showed that within V1 there was an increase in the spatial extent of activation with increasing stimulus contrast, but no trend was seen within extrastriate. In both V1 and extrastriate, the local mean activation level for all activated image pixels remained constant with increasing luminance contrast. However, when we investigated activated pixels common to all luminance contrast levels, we found that there was an increase in the mean activation level within V1, but not within extrastriate. These results suggest that there is an increase in the activity of cells in V1 with increasing luminance contrast.     

Beyond pictures and words: Alternative information-processing models for imagery effect in verbal memory.

Presents an information-processing approach to imagery effects in verbal memory tasks. A general model of the process of forming images from verbal input is developed, based on propositional memory representations like those used in computer simulations of sentence comprehension, visual scene analysis, and image processing. The general model is then refined in several classes of alternative models that attempt to account for imagery effects, with emphasis on sentence memory results, by using different mechanisms in the general model. The major division in the alternative models is whether the facilitation produced by imagery is due to the actual storage of image information or is just a by-product of image formation or the use of high-imagery materials. Some of the models are rejected on the basis of published data. Two of the remaining models would require substantial progress in the study of sentence memory and comprehension in a way not directly related to imagery. The models most likely to be successful are those that assume that the use of imagery results in the storage of redundant information that provides alternate retrieval routes. (2 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychophysical evidence for a shared representational medium for mental images and percepts.

The intuition that imagery is similar to perception has led many psychologists to assume that imaging an object consists of activating some of the same representational structures that are activated during the perception of that object. This assumption was tested in 2 experiments with 23 undergraduates by measuring the effects of visual imagery on concurrent visual perception. The experimental task consisted of a 2-interval forced-choice detection task (no stimulus identification required) during which the S imaged a particular stimulus. In Exp I, a matching image led to better detection than a nonmatching image. Interactions between imagery and perception implied a common locus of activity, and the content-specific interactions obtained implied that the common locus consisted of representational structures. In Exp II, a matching image facilitated perception only when the image and the stimulus were in the same position, suggesting that the shared representational structures occurred at an analog level of perceptual representation. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)