Selective loss of imagery in a case of visual agnosia.

Experiments were designed to examine the imagery abilities of an agnosic patient, M.S., who has consistently shown more severe deficits in recognizing visually, and in retrieving knowledge of living as compared with non-living items. Judgements of visual similarity were required for named objects and for object-pictures, as well as for the factual properties of these stimuli. The same disproportionate difficulty in processing living ('natural') objects was found in these tasks as well as in forced-choice recognition. In contrast, no deficit was found on analogous tasks concerned with word-shape similarities. These findings have a bearing on concepts of semantic memory.     

Phantabulation: A case of visual imagery interference on visual perception

We report the case of a 52-year old man who, following rupture of an anterior communicating artery aneurysm, presented with a phenomenon not previously described, which we have labelled “Phantabulation.” Phantabulation is characterized by frequent and purposeful interactions with contextually appropriate imagined objects. We suggest that this phenomenon results from confusion between real and imagined objects, caused by failure to inhibit florid visual imagery, facilitated by cortical release mechanisms.     

Loss of imagery phenomenology with intact visuo-spatial task performance: A case of ‘blind imagination’

The capacity for imagery, enabling us to visualise absent items and events, is a ubiquitous feature of our experience. This paper describes the case of a patient, MX, who abruptly lost the ability to generate visual images. He rated himself as experiencing almost no imagery on standard questionnaires, yet performed normally on standard tests of perception, visual imagery and visual memory. These unexpected findings were explored using functional MRI scanning (fMRI). Activation patterns while viewing famous faces were not significantly different between MX and controls, including expected activity in the fusiform gyrus. However, during attempted imagery, activation in MX's brain was significantly reduced in a network of posterior regions while activity in frontal regions was increased compared to controls. These findings are interpreted as suggesting that MX adopted a different cognitive strategy from controls when performing the imagery task. Evidence from experimental tasks thought to rely on mental imagery, such as the Brooks’ matrices and mental rotation, support this interpretation. Taken together, these results indicate that successful performance in visual imagery and visual memory tasks can be dissociated from the phenomenal experience of visual imagery.     

A dissociation of conscious visual imagery and visual short-term memory

Two people who reported an impaired ability to form conscious visual images were tested. Compared to a control group of college students, these impaired visualizers were not impaired on two tests of visual short-term memory. Furthermore, they retained more digits in visual short-term memory than they could visualize. These results suggests that deficits in the ability to form conscious visual images can arise without visual short-term memory being impaired, and conscious visual imagery should not be equated with visual short-term memory.     

Temporal dynamics of the knowledge‐mediated visual disambiguation process in humans: a magnetoencephalography study

Disambiguation of a noisy visual scene with prior knowledge is an indispensable task of the visual system. To adequately adapt to a dynamically changing visual environment full of noisy visual scenes, the implementation of knowledge‐mediated disambiguation in the brain is imperative and essential for proceeding as fast as possible under the limited capacity of visual image processing. However, the temporal profile of the disambiguation process has not yet been fully elucidated in the brain. The present study attempted to determine how quickly knowledge‐mediated disambiguation began to proceed along visual areas after the onset of a two‐tone ambiguous image using magnetoencephalography with high temporal resolution. Using the predictive coding framework, we focused on activity reduction for the two‐tone ambiguous image as an index of the implementation of disambiguation. Source analysis revealed that a significant activity reduction was observed in the lateral occipital area at approximately 120 ms after the onset of the ambiguous image, but not in preceding activity (about 115 ms) in the cuneus when participants perceptually disambiguated the ambiguous image with prior knowledge. These results suggested that knowledge‐mediated disambiguation may be implemented as early as approximately 120 ms following an ambiguous visual scene, at least in the lateral occipital area, and provided an insight into the temporal profile of the disambiguation process of a noisy visual scene with prior knowledge.     

Brain areas underlying visual mental imagery and visual perception: an fMRI study

We used functional magnetic resonance imaging (fMRI) to assess the maximal degree of shared neural processing in visual mental imagery and visual perception. Participants either visualized or saw faint drawings of simple objects, and then judged specific aspects of the drawings (which could only be evaluated properly if they used the correct stimulus). The results document that visual imagery and visual perception draw on most of the same neural machinery. However, although the vast majority of activated voxels were activated during both conditions, the spatial overlap was neither complete nor uniform; the overlap was much more pronounced in frontal and parietal regions than in temporal and occipital regions. This finding may indicate that cognitive control processes function comparably in both imagery and perception, whereas at least some sensory processes may be engaged differently by visual imagery and perception.     

Reported visual imagery and apparent motion: an event-related potential study

A previous behavioral study showed that a group of individuals with high vividness of visual imagery (High group), as determined from the score for the Vividness of Visual Imagery Questionnaire (VVIQ), could perceive the apparent motion path more strongly than a group of individuals with low vividness of visual imagery (Low group). To examine the physiological differences underlying these differences in perception, we compared the brain activity during an apparent motion task for the High and the Low groups using electroencephalography. We initially screened 60 potential participants using the VVIQ. On the basis of their scores, we invited 20 people from the lower and the higher ends of the VVIQ distribution to participate in our event-related potential study. Our results showed that individuals in both the High and the Low groups were sensitive to the apparent motion content of the task. Perception of apparent motion evoked a negative potential starting around 90 ms, followed by a positive potential beginning at 150-170 ms after the second stimulus. The scalp distributions of both negative and positive potentials for the High group were broader than those for the Low group. Moreover, the onset of positivity in the High group (150 ms) was earlier than that in the Low group (170 ms). We believe that these results may be mechanistically associated with the differences in the perception of apparent motion between individuals with high and low vividness of visual imagery.     

Callosal tissue loss in multiple system atrophy—A one‐year follow‐up study

Multiple system atrophy (MSA) is a neurodegenerative disease not only affecting the basal ganglia, brainstem, cerebellum, and intermediolateral cell columns of the spinal cord but also the cerebral cortex. Clinically, cerebellar (MSA‐C) and parkinsonian variants of MSA (MSA‐P) are distinguished. We investigated 14 MSA patients (10 MSA‐C, 4 MSA‐P, men: 7, women: 7; age: 61.1 ± 3.3 years) and 14 matched controls (men: 7, women: 7; age: 58.6 ± 5.1 years) with voxel‐based morphometry (VBM) to analyze gray and white matter differences both at baseline and at follow‐up, 1 year later. Baseline comparisons between patients and controls confirmed significantly less gray matter in MSA in the cerebellum and cerebral cortex, and significantly less white matter in the cerebellar peduncles and brainstem. Comparisons of tissue‐loss profiles (i.e., baseline versus follow‐up) between patients and controls, revealed white matter reduction in MSA along the middle cerebellar peduncles, reflecting degeneration of the ponto‐cerebellar tract as a particularly prominent and progressive morphological alteration in MSA. Comparisons between baseline and follow‐up, separately performed in patients and controls, revealed additional white matter reduction in MSA along the corpus callosum at follow‐up. This was replicated through additional shape‐based analyses indicating a reduced callosal thickness in the anterior and posterior midbody, extending posteriorly into the isthmus. Callosal atrophy may possibly reflect a disease‐specific pattern of neurodegeneration and cortical atrophy, fitting well with the predominant impairment of motor functions in the MSA patients. © 2010 Movement Disorder Society     

A left hemisphere basis for visual mental imagery?

The lateralization of visual mental imagery was investigated by presenting each hemisphere of a commissurotomy patient with a letter classification task known to require imagery and with a pair of control tasks designed to require all of the same processes as the imagery task except for the imagery processing itself. Whereas both hemispheres performed well on the control tasks, only the left hemisphere performed the imagery task.     

Muscle—eye—brain disease: A neuropathological study

A combination of congenital central nervous, ocular and muscular abnormalities is characteristic of muscle—eye—brain disease (MEB), of Fukuyama congenital muscular dystrophy (FCMD), and of Walker-Warburg syndrome (WWS). The nosological relationship of these inherited malformative disorders is still unestablished, although the genetic locus for FCMD has been excluded in MEB. We present the first postmortem neuropathological study of MEB based on 2 male patients. Apart from sharply limited occipital agyric areas, their brain showed coarse gyri with an abnormally nodular surface (?cobblestone cortex”?). Both the cerebral and cerebellar cortices showed a total disorganization without horizontal lamination. The haphazardly oriented cortcal neurons formed irregular custers or islands, separated by gliovascular strands extending from the pia. The ocular abnormalities included a pronounced glial preretinal membrane. Although MEB shares the cobblestone cortex—type malformation with FCMD and WWS, the cerebral and ocular manifestations are less severe than in WWS. Furthermore, a consistently weak staining for laminin α2 chain (merosin) was found in muscle biopsy specimens from 4 MEB patients, while normal immunoreactivity was observed for the laminin α2 chain, reported to be severely deficient in WWS. These finding support nosological independence of MEB.     

Brain activity during visual versus kinesthetic imagery: an fMRI study

Although there is ample evidence that motor imagery activates similar cerebral regions to those solicited during actual movements, it is still unknown whether visual (VI) and kinesthetic imagery (KI) recruit comparable or distinct neural networks. The present study was thus designed to identify, through functional magnetic resonance imaging at 3.0 Tesla in 13 skilled imagers, the cerebral structures implicated in VI and KI. Participants were scanned in a perceptual control condition and while physically executing or focusing during motor imagery on either the visual or kinesthetic components of an explicitly known sequence of finger movements. Subjects' imagery abilities were assessed using well-established psychological, chronometric, and new physiological measures from the autonomic nervous system. Compared with the perceptual condition, physical executing, VI, and KI resulted in overlapping (albeit non-identical) brain activations, including motor-related regions and the inferior and superior parietal lobules. By contrast, a divergent pattern of increased activity was observed when VI and KI were compared directly: VI activated predominantly the occipital regions and the superior parietal lobules, whereas KI yielded more activity in motor-associated structures and the inferior parietal lobule. These results suggest that VI and KI are mediated through separate neural systems, which contribute differently during processes of motor learning and neurological rehabilitation.     

Selective deficit of mental visual imagery with intact primary visual cortex and visual perception

There is a vigorous debate as to whether visual perception and imagery share the same neuronal networks, whether the primary visual cortex is necessarily involved in visual imagery, and whether visual imagery functions are lateralized in the brain. Two patients with brain damage from closed head injury were submitted to tests of mental imagery in the visual, tactile, auditory, gustatory, olfactory and motor domains, as well as to an extensive testing of cognitive functions. A computerized mapping procedure was used to localize the site and to assess the extent of the lesions. One patient showed pure visual mental imagery deficits in the absence of imagery deficits in other sensory domains as well as in the motor domain, while the other patient showed both visual and tactile imagery deficits. Perceptual, language, and memory deficits were conspicuously absent. Computerized analysis of the lesions showed a massive involvement of the left temporal lobe in both patients and a bilateral parietal lesion in one patient. In both patients the calcarine cortex with the primary visual area was bilaterally intact. Our study indicates that: (i) visual imagery deficits can occur independently from deficits of visual perception; (ii) visual imagery deficits can occur when the primary visual cortex is intact and (iii) the left temporal lobe plays an important role in visual mental imagery.     

Additional considerations in the cognitive-behavioral treatment of obsessional ruminations — A case study

The cognitive-behavioral treatment of a 24-year-old woman with moderately severe obsessional ruminations is described. The case demonstrates both the effectiveness and limitations of exposure with response prevention techniques for obsessive-compulsive disorder. The client's response raises questions about the clinical utility of viewing obsessions exclusively as conditioned anxiety stimuli. In addition, the case shows that cognitions related to control rather than appraisals of responsibility were instrumental in initiating neutralising activity. Further modification of the current cognitive-behavioural hypotheses regarding obsessions in recommended.     

A case of SSPE presenting visual disturbance and serial MRI study]

A case of subacute sclerosing panencephalitis (SSPE) was reported. The patient was a 16-year-old boy and he initially developed visual disturbance. His neurologic symptoms were myoclonus, dementia, and visual disturbance which was rare as an initial symptom in SSPE. Fundoscopy revealed bilateral pole chorioretinitis and macular degeneration. Serial MRI study demonstrated the lesions in the brain and right eye ball. The distribution varied as time went on. T2-weighted MR images showed the lesions more clearly than T1-weighted MR images. In this case dementia was marked but the lesions in the cerebrum on the MR images were considerably smaller than expected. Although MR image is useful to show the lesions, the discrepancy between clinical signs and MR images may be present in the early stage in SSPE.     

Neural networks for internal reading and visual imagery of reading: a PET study

Regional cerebral blood flow (rCBF) measurements with positron emission tomography (PET) were made on 10 volunteers in rest condition as well as while the subjects, with closed eyes, (i) internally listed the letters of the alphabet and cited the first verse of the Hungarian national anthem, (ii) visualised the capital letters of the alphabet, and (iii) visualised the capital letters of the first verse of the Hungarian national anthem. Significant changes in rCBF indicated various networks of cortical neuronal populations active during the tasks. Internal listing, as compared to the rest condition, activated the left precentral gyrus. Visualising the letters of the alphabet, when compared to the rest condition, activated a cortical network comprising fields along the banks of the left and right intraparietal sulci, the left medial frontal, precentral and occipital sulci, and the right superior frontal gyrus. Visualising the letters of the anthem, when compared to the rest condition, activated a cortical network comprising fields along the banks of the left and right intraparietal sulci, the left medial and inferior frontal gyri, and the right anterior cingulate gyrus. Contrasting the two visualisation tasks revealed task specific activation in the left lateral occipital gyrus (alphabet vs. anthem visualisation) and in the left anterior cingulate gyrus (anthem vs. alphabet visualisation). The data indicate that visual imagery of letters of the alphabet or a text engages a widespread network of cortical fields in the visual association cortices and the frontal cortex, without the engagement of the primary (V1) and secondary (V2) visual cortical areas. This finding supports the hypothesis that neuronal populations engaged by visual imagery and visual perception only partially overlap. The networks, activated in the visualisation tasks, have a core which is identical in the different visualisation tasks. The core network is complemented in a task-specific manner by the recruitment of additional cortical neuronal populations.     

Neural substrates of animal mental imagery: calcarine sulcus and dorsal pathway involvement — an fMRI study

Neural response was measured using fMRI in six healthy volunteers, performing a mental imagery task, using verbal cues exclusively. They listened to a list of animal names from which to generate a mental image, and listened passively to a list of abstract words. They were tested twice, using the same protocol. SPM99-processed results showed for both sessions activation in the calcarine sulcus and local activation foci, mainly in the occipito-parietal region. Other studies involving figurative mental imagery using verbal cues, have shown activation in the occipito-temporal area, but none in the calcarine sulcus or in the dorsal route. We account for the discrepancies relative to previous mental imagery studies using verbal cues, in terms of differences in the experimental conditions. In our opinion, restricting the stimuli to a single semantic category (animals) and increasing the time dedicated to the production of MI, may have enhanced the components of the pictures. This mental imagery generation protocol shows the importance of the design of experimental tasks on anatomo-functional responses.     

A study of visual processes in a case of interhemispheric disconnexion

A 75-year-old right-handed woman, after a probable cerebral infarct, developed an irregular constriction of the visual fields, a left-sided agraphia, and an anomia for objects in the left hand. Subsequent testing demonstrated an inability to name, though ability to recognize, letters and objects flashed in the homonymous left visual field. An inter-hemispheric disconnexion syndrome was inferred from these findings. The present publication concerns mainly the visual aspects of this disconnexion syndrome.Tasks were devised to test the abilities of the major and minor hemisphere: (a) the left hemisphere demonstrated a complete dominance for language expression and an incomplete dominance for written language comprehension; (b) the right hemisphere appeared to be dominant for some visuo-spatial tasks including number comprehension; (c) when the hemispheres were given contradictory visual informations on a non-verbal task (chimeric stimuli) there was a predominance of the right hemisphere. The right hemisphere appeared able to process complex information. Specialization of functional activities in each hemisphere is briefly discussed.     

A case of naturally occurring visual field loss in a chimpanzee with an arachnoid cyst

Deficits in the occipital cortex have varying consequences among mammalian species. Such variations are indicative of evolutionary transitions in the striate cortical contribution to visually guided behavior. However, little is known about the role of the striate cortex in visually guided behavior in chimpanzees due to ethical concerns about invasive experiments and methodological limitations such as the inability to monitor gaze movements. We had the opportunity to study the behavioral consequences of a deficit in the occipital cortex in a chimpanzee with a naturally occurring arachnoid cyst in her right occipital lobe. We assessed the chimpanzee's ability to detect a small light probe (0.5 visual degree, Michelson contrast>0.9) presented at several locations in the visual field while monitoring gaze direction using an infra-red remote eye-tracker recently introduced to studies of great apes. The results showed the chimpanzee was unable to detect the probe in the lower left quadrant of the visual field, suggesting severe loss of contrast sensitivity in a part of hemivisual field that is retinotopically corresponded to the hemisphere of the cyst. A chimpanzee with a naturally occurring deficit in the right striate cortex and the availability of remote eye-tracking technology presented a unique opportunity to compare the role of the occipital lobe in visually guided behavior among various primate species.