Visual Processing without Awareness: Evidence from Unilateral Neglect

Berti, Anna Emilia; Rizzolatti, Giacomo

doi:10.1162/jocn.1992.4.4.345

Cited by 280 publications

(139 citation statements)

References 26 publications

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“…Neglect patients fail to explicitly detect stimuli presented in the contralesional aVected Weld. However, they can implicitly process the same stimuli up to the semantic level (Berti and Rizzolatti 1992;Berti et al 1994). Brain imaging experiments are being carried out to assess which brain circuits underpin the implicit and explicit access routes for body knowledge.…”

Section: Discussionmentioning

confidence: 99%

Bodily self: an implicit knowledge of what is explicitly unknown

et al. 2011

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We tested the hypothesis that the body selfadvantage, i.e., the facilitation in discriminating self versus other people's body-eVectors, is the expression of an implicit and body-speciWc knowledge, based mainly on the sensorimotor representation of one's own body-eVectors. Alternatively, the body self-advantage could rely on visual recognition of pictorial cues. According to the Wrst hypothesis, using gray-scale pictures of body-parts, the body selfadvantage should emerge when self-body recognition is implicitly required and should be speciWc for body-eVectors and not for inanimate-objects. In contrast, if the self-advantage is due to a mere visual-perceptual facilitation, it should be independent of the implicit or explicit request (and could be extended also to objects). To disentangle these hypotheses, healthy participants were implicitly or explicitly required to recognize either their own body-eVectors or inanimate-objects. Participants were more accurate in the implicit task with self rather than with others' bodyeVectors. In contrast, the self-advantage was not found when an explicit recognition of one's own body-eVectors was required, suggesting that the body self-advantage relies upon a sensorimotor, rather than a mere visual representation of one's own body. Moreover, the absence of both self/ other and implicit/explicit eVects, when processing inanimate-objects, underlines the diVerences between the body and other objects.

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Section: Discussionmentioning

confidence: 99%

Bodily self: an implicit knowledge of what is explicitly unknown

et al. 2011

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“…What is it then that prevents the patient from sticking them together? Berti and Rizzolatti (1992) propose that the encoding of space is a necessary prerequisite for conscious perception. If spatial encoding is prevented or impaired, as it is in neglect, the presence of the stimulus does not enter consciousness.…”

Section: Beyond Space: a Dissociation In Timementioning

confidence: 99%

Time and neglect: Abnormal temporal dynamics in unilateral spatial neglect

Becchio

Bertone²

2006

Neuropsychologia

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Temporality enters our immediate experience as passage and becoming: the role time plays in the construction of a world of enduring entities tends to go unnoticed. This paper examines the relation between time and ontology in the context of unilateral neglect, a neuropsychological syndrome in which patients fail to perceive or respond to stimuli in the contralateral hemifield, behaving as if that half of space does not exist. Traditional models characterize neglect exclusively in spatial terms. Based on recent investigations suggesting abnormal temporal dynamics, here we highlight the impact of time factors on the presentation of the disorder. Neglect patients do not simply miss the presence of stimuli on the left: they also ignore the past as well as the future of neglected stimuli. We claim that, if this occurs, it is because time, and not only space, is impaired. Torino, 05/05/2006Dear Editor, We modified the manuscript in an attempt to achieve the top standard required for publication in Neuropsychologia. Reviewer 1The reviewers have answered most of my concerns to my satisfaction. However, there is still a onesentence paragraph on page 3, and the formatting appears to need revision on page 17.We would like to thank the reviewer for her/his careful review of our manuscript. We have now integrated the one-sentence paragraph on page 3. Formatting on page 17 has been revised.On page 10, there is a typing mistake: the word "that" should be replaces by "than" in the second to last paragraph.We apologize for the typing mistake. As requested we have now replaced "that". These bewildering behavioural manifestations clearly exhibit a spatial gradient: the patient behaves as if half of the space does not exist, failing to report, react or search for stimuli located in the space contralateral to the lesion. The spatial nature of neglect is manifest and, understandably, interest in research has focused on spatial mechanisms (Halligan, Fink, Marshall, & Vallar, 2003).Here, we intend to focus on a dimension that, although less evident, is nevertheless no less important in the presentation of the disorder: time.Compared with spatial cognition, little is known about the neuropsychology of time. In this paper we first summarize the results of recent investigations suggesting abnormal temporal dynamics in neglect. Next, we consider some of the empirical and theoretical issues raised by this evidence: do the temporal abnormalities observed in neglect reflect the impairment of a unique mechanism or do they arise in relation to different timing systems? Do temporal deficits in neglect relate to spatial distortions? A final concern relates to the contribution of temporal deficits to neglect per se, i.e. to the loss of awareness for contralateral stimuli and events characteristically observed in neglect patients. It is impossible for us -wrote Kant in the Critique of Pure Reason (1787) -to represent things outside space and time and this is because things appear to us as spatiotemporally connoted. Whereas previous work f...

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“…6 and 7) and semantic priming (e.g., ref. 8). It has been speculated (3,9) that such effects might relate to separate cortical visual streams, with temporal areas extracting object features for identification, and parietal areas encoding spatial locations and parameters for action (10).…”

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confidence: 99%

Neural fate of seen and unseen faces in visuospatial neglect: A combined event-related functional MRI and event-related potential study

Vuilleumier

Sagiv

Hazeltine

et al. 2001

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

196

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To compare neural activity produced by visual events that escape or reach conscious awareness, we used event-related MRI and evoked potentials in a patient who had neglect and extinction after focal right parietal damage, but intact visual fields. This neurological disorder entails a loss of awareness for stimuli in the field contralateral to a brain lesion when stimuli are simultaneously presented on the ipsilateral side, even though early visual areas may be intact, and single contralateral stimuli may still be perceived. Functional MRI and event-related potential study were performed during a task where faces or shapes appeared in the right, left, or both fields. Unilateral stimuli produced normal responses in V1 and extrastriate areas. In bilateral events, left faces that were not perceived still activated right V1 and inferior temporal cortex and evoked nonsignificantly reduced N1 potentials, with preserved face-specific negative potentials at 170 ms. When left faces were perceived, the same stimuli produced greater activity in a distributed network of areas including right V1 and cuneus, bilateral fusiform gyri, and left parietal cortex. Also, effective connectivity between visual, parietal, and frontal areas increased during perception of faces. These results suggest that activity can occur in V1 and ventral temporal cortex without awareness, whereas coupling with dorsal parietal and frontal areas may be critical for such activity to afford conscious perception. R ight parietal damage may cause a loss of awareness for contralateral (left) sensory inputs, such as hemispatial neglect and extinction (1-3). Visual extinction is the failure to perceive a stimulus in the contralesional field when presented together with an ipsilesional stimulus (bilateral simultaneous stimulation, BSS), even though occipital visual areas are intact and unilateral contralesional stimuli can be perceived when presented alone. It reflects a deficit of spatial attention toward the contralesional side, excluding left inputs from awareness in the presence of competing stimuli (2, 3). Spatial attention involves a complex neural network centered on the right parietal lobe (4, 5), but how parietal and related areas interact with sensory processing in distant cortices is largely unknown.Here we combined event-related functional MRI (fMRI) and event-related potentials (ERPs) to study the regional pattern and temporal course of brain activity produced by seen and unseen stimuli in a patient with chronic neglect and extinction caused by parietal damage. In keeping with intact early visual areas in such patients, behavioral studies suggest that some residual processing may still occur for contralesional stimuli without attention, or without awareness, including ''preattentive'' grouping (e.g., refs. 6 and 7) and semantic priming (e.g., ref. 8). It has been speculated (3, 9) that such effects might relate to separate cortical visual streams, with temporal areas extracting object features for identification, and parietal areas encoding spatial...

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Visual Processing without Awareness: Evidence from Unilateral Neglect

Cited by 280 publications

References 26 publications

Bodily self: an implicit knowledge of what is explicitly unknown

Bodily self: an implicit knowledge of what is explicitly unknown

Time and neglect: Abnormal temporal dynamics in unilateral spatial neglect

Neural fate of seen and unseen faces in visuospatial neglect: A combined event-related functional MRI and event-related potential study

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