Image generation from long-term memory in Parkinson's disease.
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Basal Ganglia Diseases↗
Biomedical subjects
S M Kosslyn
Publications and source records attributed to S M Kosslyn.
Topographical representations of mental images in primary visual cortex.
We report here the use of positron emission tomography (PET) to reveal that the primary visual cortex is activated when subjects close their eyes and visualize objects. The size of the image is systematically related to the location of maximal activity, which is as expected because the earliest visual areas are spatially organized. These results were only evident, however, when imagery conditions were compared to a non-imagery baseline in which the same auditory cues were presented (and hence the stimuli were controlled); when a resting baseline was used (and hence brain activation was uncontrolled), imagery activation was obscured because of activation in visual cortex during the baseline condition. These findings resolve a debate in the literature about whether imagery activates early visual cortex and indicate that visual mental imagery involves 'depictive' representations, not solely language-like descriptions. Moreover, the fact that stored visual information can affect processing in even the earliest visual areas suggests that knowledge can fundamentally bias what one sees.
Brain Mapping↗
Brain mechanisms in human classical conditioning: a PET blood flow study.
Five healthy male subjects participated in a classical conditioning experiment, and positron emission tomography (PET) was used to compare regional cerebral blood flow before and after conditioning. The subjects participated in three different experimental phases. In the first (habituation) phase they listened to 24 repetitions of a tone with random intervals. In the second (acquisition) phase, the tone was paired with a brief shock to the wrist. In the third (extinction) phase, the tone was presented alone again. 15OPET scans were taken during the habituation and extinction phases. Because the habituation and extinction phases were similar, any difference in blood flow to the tones presented during extinction probably reflected conditioning that occurred during the acquisition phase. Statistical parametric mapping (SPM) analysis of the PET data showed significantly increased activation in the right hemisphere in the orbito-frontal cortex, dorsolateral prefrontal cortex, inferior and superior frontal cortices, and inferior and middle temporal corticies. The only activated areas in the left hemisphere were area 19 and the superior frontal cortex. The results are interpreted as evidence for the involvement of cortical areas in human classical conditioning.
Acoustic Stimulation↗
The perception of curvature can be selectively disrupted in prosopagnosia.
A brain-damaged patient with prosopagnosia and a group of age- and education-matched control subjects evaluated curved and straight versions of different sorts of stimuli in different tasks. The patient consistently required more time to encode curved than straight stimuli, relative to the control subjects. Specifically, he had a deficit when he compared curved lines that were simultaneously visible, when he compared curved lines with those previously seen, when he examined a curved shape to determine whether an X was on or off the shape, and when he read curved script. He also made more errors when he named pictures of curved objects. Implications of these findings for some types of clinical disorders and for the role of "end-stopped" cells in visual cortex are discussed.
Adolescent↗
The cognitive neuroscience of mental imagery.
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Cognition↗
Two types of image generation: evidence for left and right hemisphere processes.
The results from seven experiments provide evidence that visual mental images can be generated by either the left or right cerebral hemisphere, but in different ways. Subjects were cued to form images within a grid or within a set of four corner brackets; a single X mark was enclosed within each stimulus, and the subjects were to determine whether the X mark was enclosed within each stimulus, and the subjects were to determine whether the X mark would have fallen on an imaged pattern. When subjects memorized descriptions of how parts were arranged, they could later form images of the composite pattern when cued in the right visual field (left hemisphere) more accurately than when they were cued in the left visual field (right hemisphere). In contrast, when subjects memorized individual segments on a screen, and 'mentally glued' them into a single pattern, they later could form images more accurately, at least in some circumstances, when cued in the left visual field. These results were predicted by the theory that images are built up by arranging parts, and that two different processes can be used to arrange them. One process uses stored descriptions to arrange parts, and is more effective in the left cerebral hemisphere; the other process uses stored memories of metric positions to arrange parts, and is more effective in the right cerebral hemisphere. Convergent evidence was obtained by having subjects memorize letters in grids (which are easily encoded using descriptions of the positions of segments) or within a space delineated by four brackets (which require memorizing the precise positions of the segments). Subjects were relatively more accurate when cued in the left visual field with bracket stimuli, but tended to be relatively more accurate when cued in the right visual field with grids stimuli. Control experiments showed that this finding was not due to hemispheric differences in the ease of forming images at different sizes or differences in the ease of perceptually encoding the probes.
Adolescent↗
On computational evidence for different types of spatial relations encoding: reply to Cook et al. (1995).
Computational models in psychology play an increasingly important role in characterizing theoretical distinctions, understanding empirical results, and formulating new predictions. However, the proper use of models is subject to debate and interpretation, as Cook, Früh, and Landis (1995) have demonstrated in a critique of neural network simulations reported by Kosslyn, Chabris, Marsolek, and Koenig (1992). These simulation results supported a distinction between two types of spatial relations encoding. Cook et al. argue that Kosslyn et al.'s models did not process "spatial" representations and that input-output correlations rather than properties of spatial relations encoding processes explain the performance of the models. This article provides conceptual and analytic rebuttals of those criticisms.
Brain↗
Visual processing in migraineurs.
Twelve migraine subjects with aura and 12 matched control subjects performed four computerized visual tasks. Because chronic electroencephalographic and regional cerebral blood flow abnormalities in posterior brain functions have been documented during interictal periods, migraine subjects were tested between migraine attacks. Two tasks, orientation detection and temporal order judgement, were devised to examine 'low-level' visual processes. The results were compared with results from two tasks, picture naming and word priming, that were devised to examine 'high-level' visual processes. Regarding the response time data across all four tasks, the migraine group was faster in the two low-level tasks. There were no differences in error rate in any of the four tasks. The migraineur's apparent response time advantage in the low-level tasks provides a psychophysical corroboration of their assumed oversensitivity to visual stimuli. The remaining two tasks, picture naming and word priming, which involve the use of previously stored information, do not distinguish migraineurs from matched control subjects. These results suggest that migraineurs are better in low-level visual processing, in that the signals to the primary visual cortex (Area V1) are processed more rapidly, but this hypersensitivity does not carry over to the subsequent processing stages (beyond V1 to superior parietal and inferior temporal cortices), as evidenced by the absence of a response time advantage in the two higher-level vision tasks.
Adult↗
When does "no" really mean "yes"? A case study in unilateral visual neglect.
A patient with unilateral visual neglect indicated whether a dot was or was not present in a display. When present, the dot appeared equally often in the left and right visual fields. Although he typically denied having seen dots in his left visual field, he was able to make this judgment much more quickly than when no dot was in fact present. The mean response times when the dot was present (1135 and 1004 msec, for left and right) were almost twice as fast as the response times when no dot was present (2025 msec). This result suggests that the patient searched the visual fields individually, and in fact generated a "No" response based on detecting the dot in his neglected field. Thus, the mechanisms used to detect stimuli apparently are not rigidly linked to those used to classify them or to produce a response.
Acoustic Stimulation↗
In search of occipital activation during visual mental imagery.
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Eidetic Imagery↗
Mental imagery and aging.
Young adult and elderly 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, 1 by 1) 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 response times 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 imaging processes are affected selectively by aging.
Adolescent↗
Identifying objects seen from different viewpoints. A PET investigation.
Positron emission tomography scans were acquired when subjects performed three tasks, each in a separate block of trials. They decided whether words named pictures of objects viewed from a canonical perspective, decided whether words named pictures of objects viewed from a non-canonical (unusual) perspective or saw random patterns of lines and pressed a pedal when they heard the word (this was a baseline condition). The dorsolateral prefrontal region was activated when subjects identified objects seen from non-canonical perspectives, as expected if the frontal lobes are involved in top-down perceptual processing. In addition, several areas in the occipital, temporal and parietal lobes were selectively activated when subjects identified objects seen from non-canonical perspectives, as specifically predicted by a recent theory. Overall, the pattern of results supported the view that the human brain identifies objects by using a system of areas similar to that suggested by studies of other primates.
Adolescent↗
Can patients with obsessive-compulsive disorder discriminate between percepts and mental images? A signal detection analysis.
Signal detection analysis was used to test three hypotheses for repetitive thoughts and behaviors characteristic of obsessive-compulsive disorder (OCD). Patients might have (a) low sensitivity for the difference between having seen something or having imagined seeing it, (b) a high criterion for this discrimination, or (c) difficulty associating context with information in memory. Subjects judged viewed words or imagined words and later indicated which were actually seen. Patients with OCD discriminated seen from imaged words significantly better than normal control subjects, as evidenced by higher d' scores on a recognition memory task. Groups did not differ in response criterion, beta, used to decide whether words had been seen or imaged. Implications for the study of OCD from an information-processing perspective are discussed.
Adolescent↗
Visual imagery and visual-spatial language: enhanced imagery abilities in deaf and hearing ASL signers.
The ability to generate visual mental images, to maintain them, and to rotate them was studied in deaf signers of American Sign Language (ASL), hearing signers who have deaf parents, and hearing non-signers. These abilities are hypothesized to be integral to the production and comprehension of ASL. Results indicate that both deaf and hearing ASL signers have an enhanced ability to generate relatively complex images and to detect mirror image reversals. In contrast, there were no group differences in ability to maintain information in images for brief periods or to imagine objects rotating. Signers' enhanced visual imagery abilities may be tied to specific linguistic requirements of ASL (referent visualization, topological classifiers, perspective shift, and reversals during sign perception).
Adult↗
The role of the corpus callosum in the representation of lateral orientation.
How do people recognize objects when they face in a novel lateral (left/right) orientation? The results of three experiments with a split-brain patient, who has a totally nonfunctional corpus callosum, demonstrate that the corpus callosum cannot play a critical role in allowing one to recognize mirror-reversed objects. First, both cerebral hemispheres could recognize mirror-reversed versions of pictures as accurately as the original renditions in an incidental memory task. Second, when asked to decide whether pictures faced the same way that they had originally, neither hemisphere performed better than chance in an incidental memory task--suggesting that the shape representations in the hemispheres do not specify lateral orientation. Third, neither hemisphere exhibited "priming" for lateral orientation, as assessed in an "object decision task", and only the left hemisphere exhibited priming for encoding the shape (independent of its lateral orientation).
Adult↗
Cerebral lateralization.
Recent findings suggest that cerebral laterality will not be understood in terms of simple dichotomies, such as the idea that the left hemisphere is analytic and the right holistic. Rather, hemisphere differences can be better explained in terms of relatively specific principles that extend over limited domains. For visual perception and mental imagery, the left hemisphere appears to be relatively better than the right at encoding component parts, representing visual categories, and encoding categorical spatial relations; in contrast, the right hemisphere appears to be relatively better at encoding overall patterns, representing specific instances, and encoding coordinate metric spatial relations. Recent neural network models support a hypothesis that ties together these disparate findings.
Dominance, Cerebral↗
The role of parts and spatial relations in object identification.
An investigation of the role of parts and their spatial relations in object identification is reported. At the most general level, two important results were obtained. First, proper spatial relations among components of an object are critical for easy identification. When parts were scrambled on the page, naming times and error rates increased. And, second, the way an object is divided into parts (parsed) affects identification only under the most impoverished viewing conditions. When subjects had as little as 1 s (and sometimes as little as 200 ms) to view an object, the way objects were divided into parts had no effect on naming times or accuracy. There was no hint of an interaction between type of parse and how parts were arranged on the page. This pattern of effects supports theories that suggest that objects typically are recognized without being parsed into parts. The findings are in agreement with theories suggesting that object features (not specifically related to parts) are matched directly with such features stored in long-term memory, with the constraint that the features of a single object are seen from a single viewpoint.
Adult↗
The status of cognitive neuroscience.
Cognitive neuroscience rests on findings, methods, and theory from three fields: experimental psychology, systems-level neuroscience, and computer science. The strong trend over the past few years has been for a greater integration across these fields. The influence of this interdisciplinary approach on current research on memory, perception, and language will be illustrated.
Animals↗