Visual perception without awareness in a patient with posterior 
cortical atrophy: Impaired explicit but not implicit processing 
of global information

Filoteo, J. Vincent; Friedrich, Frances J.; Rabbel, Catherine; Stricker, John L.

doi:10.1017/s135561770281325x

Cited by 15 publications

(17 citation statements)

References 84 publications

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“…Mackenzie Ross et al [23] and Galton et al [11] proposed dividing PCA into subtypes, which are distinguishable at onset but tend to merge as the disease progresses: (A) predominantly occipito-temporal with visual agnosia, (B) predominantly parietal with deficits of visuo-spatial cognition and (C) a "primary visual failure" subtype with early visual-perceptual deficits. Seven of our cases can be assigned to subtype B (2 to 6,8,9). One of them had additional early disturbances of vision and developed hemianopia (no.…”

Section: Discussionmentioning

confidence: 92%

“…2). Nestor et al [26] observed similar hypometabolism in frontal areas related to the control of eye movements (Brodman areas 6,8). As they pointed out, this finding may represent a remote effect due to deafferentation, caused by the degeneration of projecting fiber from posterior visual association areas.…”

Section: ■ Imaging Findingsmentioning

confidence: 85%

“…Some authors do not differentiate between imaging-and neuropsychology-guided concepts of PCA [8,20,24,31]. There is obviously a large overlap between cases that fit into either definition, but ■ Abstract Nine patients with posterior cortical atrophy (PCA), a rare degenerative brain disease of unclear etiology and nosology, were followed over a mean time of 7.4 years.…”

Section: Introductionmentioning

confidence: 99%

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Posterior cortical atrophy: variant of Alzheimer?s disease?

2005

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Nine patients with posterior cortical atrophy (PCA), a rare degenerative brain disease of unclear etiology and nosology, were followed over a mean time of 7.4 years. The mean age at onset was low (56.2 years). At onset, eight patients had visuo-spatial and eight had memory impairment. A minority showed early signs of occipital lobe involvement with visual agnosia or hemianopia. Eight patients developed dementia after a mean course of five years. 18F-FDG-PET data of six patients were analysed with statistical parametric mapping. They showed hypometabolism centred on the lateral and medial parietal associative cortex, with variable involvement of the adjacent temporal and occipital associative cortex. A minority showed involvement of the frontal lobes, possibly related to deafferenting of areas related to the control of eye movements. Atrophy and hypometabolism were markedly asymmetric in a subset of cases. Autopsy was performed in one patient. Presenile onset, location, and asymmetry of atrophy suggest that PCA represents a biologically separable variant of Alzheimer's disease.

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Section: Discussionmentioning

confidence: 92%

Section: ■ Imaging Findingsmentioning

confidence: 85%

Section: Introductionmentioning

confidence: 99%

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Posterior cortical atrophy: variant of Alzheimer?s disease?

2005

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“…As noted, there are a few reports of “implicit” visual processing in the setting of dorsal visual stream dysfunction (Coslett & Saffran, 1991; Coslett et al, 1995; Filoteo et al, 2002; Stark et al, 1997; Wojciulik & Kanwisher, 1998). The most recent of these was a case study reported by Filoteo and colleagues (2002).…”

Section: Introductionmentioning

confidence: 99%

Recognition without awareness in a patient with simultanagnosia

Denburg

Jones

Tranel

2009

International Journal of Psychophysiology

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We report a psychophysiological study of "recognition without awareness" in patient 2354, who had severe but circumscribed atrophy in the occipitoparietal region bilaterally (caused by visual-variant Alzheimer's disease, documented by structural and functional neuroimaging) and an accompanying Balint syndrome that prevented her from recognizing the emotional valence of many highly charged negative visual scenes (e.g., a burned body). Despite this lack of overt recognition, patient 2354 nonetheless generated large amplitude skin conductance responses to highly charged negative pictures, demonstrating the same kind of recognition without awareness that has been reported previously in patients with bilateral occipitotemporal dysfunction and prosopagnosia (e.g., . Our case complements both previous evidence of covert, nonconscious recognition in patients with prosopagnosia, and previous behavioral studies of patients with Balint syndrome that have shown evidence of "preattentive" visual processing. The findings add to the small but important set of empirical observations regarding nonconscious visual processing in neurological patients, and indicate that recognition without awareness can occur in the setting of dorsal visual stream dysfunction and Balint syndrome. The findings in our patient suggest that she has patent pathways from higher order visual cortices to autonomic effectors in amygdala or hypothalamus, even though the results of such information processing are not made available to conscious awareness.

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“…These studies have most often been motivated by questions of levels of visual awareness: If ''neglected'' distractors interfere with per-ceptual processing or motor responses, then patients must process them implicitly, even when explicit recognition is impaired (66)(67)(68)(69)(70)(71)(72)(73). The focus of these studies has been to investigate whether equivalent distractor interference effects might be obtained with intact vs. damaged parietal cortex.…”

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confidence: 99%

Posterior parietal cortex and the filtering of distractors

Friedman‐Hill

Robertson

Desimone

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

167

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Neural systems for visual processing can focus attention on behaviorally relevant objects, filtering out competing distractors. Neurophysiological studies in animals and brain imaging studies in humans suggest that such filtering depends on top-down inputs to extrastriate visual areas, originating in structures important for attentional control. To test whether the posterior parietal cortex may be a necessary source of signals that filter distractors, we measured the ability of a patient with bilateral parietal lesions to discriminate the features of a target surrounded by distractors of variable contrast. In the presence of distractors, the patient was impaired at discriminating both grating orientation and faces, and the magnitude of the impairment increased with distractor salience. These attentional deficits are remarkably similar to those caused by damage to monkey extrastriate regions V4 and͞or TEO, which are thought to be recipients of top-down attentional feedback. In contrast to the effects of V4 and TEO lesions, however, the parietal lesions impaired performance even with widely spaced targets and distractors, a finding consistent with the projections of parietal cortex to visual processing areas covering a wide range of receptive field sizes and eccentricities.A typical visual scene contains many different objects, not all of which can be fully processed at any given moment. Attentional mechanisms are therefore needed to focus visual processing on the most behaviorally relevant stimuli and to filter out competing distractors. A possible mechanism for this resolution of competition between objects has been described in ventral stream visual areas of monkeys, where neurophysiological studies have found that in the absence of attention, multiple stimuli in the receptive field (RF) of a cell will compete for the response of the cell. However, when attention is directed to a target stimulus in the RF, responses are biased in favor of the target, and the influence of distracting stimuli in the RF is filtered out (1-11). Likewise, brain imaging studies in humans show a similar biasing of competition in favor of attended stimuli (12)(13)(14)(15)(16)(17)(18)(19)(20), and human subjects often experience little awareness for distractor stimuli outside the focus of attention (21-23).Lesion data also support the idea that ventral stream areas are sites where top-down inputs bias the competition in favor of attended targets compared with unattended distractors. Both monkeys with lesions of areas V4 and͞or TEO and humans with lesions of area V4 are impaired at visual discrimination tasks when target stimuli are presented in the presence of salient visual distractors (24)(25)(26). Consistent with the neurophysiological data, the attentional filtering impairments after these extrastriate lesions are limited to configurations in which both the targets and distractors are located close to one another, within an area equal to the average size of V4 and͞or TEO RFs. When normal filtering mechanisms are compromised, the pre...

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Visual perception without awareness in a patient with posterior cortical atrophy: Impaired explicit but not implicit processing of global information

Cited by 15 publications

References 84 publications

Posterior cortical atrophy: variant of Alzheimer?s disease?

Posterior cortical atrophy: variant of Alzheimer?s disease?

Recognition without awareness in a patient with simultanagnosia

Posterior parietal cortex and the filtering of distractors

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