Do visual illusions probe the visual brain? Illusions in action without a dorsal visual stream

Visual illusions have been shown to affect perceptual judgements more so than motor behaviour, which was interpreted as evidence for a functional division of labour within the visual system. The dominant perception-action theory argues that perception involves a holistic processing of visual objects or scenes, performed within the ventral, inferior temporal cortex. Conversely, visuomotor action involves the processing of the 3D relationship between the goal of the action and the body, performed predominantly within the dorsal, posterior parietal cortex. We explored the effect of well-known visual illusions (a size-contrast illusion and the induced Roelofs effect) in a patient (IG) suffering bilateral lesions of the dorsal visual stream. According to the perception-action theory, IG's perceptual judgements and control of actions should rely on the intact ventral stream and hence should both be sensitive to visual illusions. The finding that IG performed similarly to controls in three different illusory contexts argues against such expectations and shows, furthermore, that the dorsal stream does not control all aspects of visuomotor behaviour. Assuming that the patient's dorsal stream visuomotor system is fully lesioned, these results suggest that her visually guided action can be planned and executed independently of the dorsal pathways, possibly through the inferior parietal lobule.     

Appropriate stimulation in visual evoked potential to evaluate visual perception state of athletes★

BACKGROUND: Several studies have demonstrated that visual evoked potentials can be influenced by sport events. To the best of our knowledge, there are no specific parameters for the most appropriate stimulation for evaluating the functional state of athletes. OBJECTIVE: To investigate the best stimulation in visual evoked potential to apply to functional evaluation of athletes. DESIGN, TIME AND SETTING: Ninety-five, healthy students from the Shandong Normal University took part in an observational, contrast study. PARTICIPANTS: All active participants were male. Sixty-five students majored in physical education, and had participated in exercise for the duration of (4.26 ± 3.08) years. An additional 30 students majored in other subjects. METHODS: The neural electricity tester, NDI-200, was adapted to examine and record visual evoked potential with varying probes using bipolar electrodes attached to the head of all the participants in a dark room. The visual evoked potential values were analyzed transversally. A chessboard pattern reversal method was applied with the following parameters: 2 Hz stimulation frequency, brightness of 90 cdp, 80% contrast, 1–100 Hz bandpass filters, and 10 μV sensitivity; 100 responses were averaged. MAIN OUTCOME MEASURES: latency, peak latencies, and inter-peak latencies were measured in N75, P100, N145 with varying probe stimulations. RESULTS: (1) Comparisons between the little check, middle check, and big check stimulation, demonstrated that the common tendencies in visual evoked potential indexes of the two groups of N75 latency were successively shorter and N145 were longer. P100-N145 peak latency was decreased and each inter-peak latency was longer. (2) Changes of N75, P100, and N145 with different check stimulations in the physical education student group: after compared with the middle check stimulation, N75 latency was significantly longer (P < 0.01), and N75-P100 inter-peak latency (P < 0.05) and N75-N145 inter-peak latency were both shorter (P < 0.05). N75-P100 inter-peak latency was shorter (P < 0.01) in the little check stimulation. When compared with the big check stimulation, N75 latency was significantly longer (P < 0.01) and N145 was shorter (P < 0.01). Compared with the big check stimulation, N145 latency was significantly shorter (P < 0.05). (3) Changes of N75, P100, and N145 with different check stimulations in the normal students: when compared with the big check stimulation, N75 latency was significantly longer (P < 0.05) and N145 latency was shorter (P < 0.05). Each inter-peak latency was shorter (P < 0.05) in the little check stimulation. When comparing the middle check stimulation, N75-N145 inter-peak latency was shorter (P < 0.05). CONCLUSION: Large visual evoked potential differences were observed between students majoring in physical education and other subjects when medium probe stimulation was applied. These results suggest that the use of medium probe stimulation (25 mm×25 mm) should be adopted when evaluating the functional state of athletes. Key Words: visual evoked potential; functional evaluation; probe stimulation     

Appropriate stimulation in visual evoked potential to evaluate visual perception state of athletes★

BACKGROUND: Several studies have demonstrated that visual evoked potentials can be influenced by sport events. To the best of our knowledge, there are no specific parameters for the most appropriate stimulation for evaluating the functional state of athletes. OBJECTIVE: To investigate the best stimulation in visual evoked potential to apply to functional evaluation of athletes. DESIGN, TIME AND SETTING: Ninety-five, healthy students from the Shandong Normal University took part in an observational, contrast study. PARTICIPANTS: All active participants were male. Sixty-five students majored in physical education, and had participated in exercise for the duration of (4.26 ± 3.08) years. An additional 30 students majored in other subjects. METHODS: The neural electricity tester, NDI-200, was adapted to examine and record visual evoked potential with varying probes using bipolar electrodes attached to the head of all the participants in a dark room. The visual evoked potential values were analyzed transversally. A chessboard pattern reversal method was applied with the following parameters: 2 Hz stimulation frequency, brightness of 90 cdp, 80% contrast, 1–100 Hz bandpass filters, and 10 μV sensitivity; 100 responses were averaged. MAIN OUTCOME MEASURES: latency, peak latencies, and inter-peak latencies were measured in N75, P100, N145 with varying probe stimulations. RESULTS: (1) Comparisons between the little check, middle check, and big check stimulation, demonstrated that the common tendencies in visual evoked potential indexes of the two groups of N75 latency were successively shorter and N145 were longer. P100-N145 peak latency was decreased and each inter-peak latency was longer. (2) Changes of N75, P100, and N145 with different check stimulations in the physical education student group: after compared with the middle check stimulation, N75 latency was significantly longer (P < 0.01), and N75-P100 inter-peak latency (P < 0.05) and N75-N145 inter-peak latency were both shorter (P < 0.05). N75-P100 inter-peak latency was shorter (P < 0.01) in the little check stimulation. When compared with the big check stimulation, N75 latency was significantly longer (P < 0.01) and N145 was shorter (P < 0.01). Compared with the big check stimulation, N145 latency was significantly shorter (P < 0.05). (3) Changes of N75, P100, and N145 with different check stimulations in the normal students: when compared with the big check stimulation, N75 latency was significantly longer (P < 0.05) and N145 latency was shorter (P < 0.05). Each inter-peak latency was shorter (P < 0.05) in the little check stimulation. When comparing the middle check stimulation, N75-N145 inter-peak latency was shorter (P < 0.05). CONCLUSION: Large visual evoked potential differences were observed between students majoring in physical education and other subjects when medium probe stimulation was applied. These results suggest that the use of medium probe stimulation (25 mm×25 mm) should be adopted when evaluating the functional state of athletes. Key Words: visual evoked potential; functional evaluation; probe stimulation     

Multimodal visual system analysis as a biomarker of visual hallucinations in Parkinson’s disease

Journal of Neurology - Visual hallucinations (VH) are present in up to 75% of Parkinson’s disease (PD) patients. However, their neural bases and participation of the visual system in VH are...     

Could visual neglect induce amblyopia?

Oculomotor nerve disease is a common cause of diplopia. When strabismus is present, absence of diplopia has to induce the research of either uncovering of visual fields or monocular suppression, amblyopia or blindness. We describe the case of a 41-year-old woman presenting with right oculomotor paresis and left object-centred visual neglect due to a right fronto-parietal haemorrhage expanding to the right peri-mesencephalic cisterna caused by the rupture of a right middle cerebral artery aneurysm. She never complained of diplopia despite binocular vision and progressive recovery of strabismus, excluding uncovering of visual fields. Since all other causes were excluded in this case, we hypothesise that the absence of diplopia was due to the object-centred visual neglect. Partial internal right oculomotor paresis causes an ocular deviation in abduction; the image being perceived deviated contralaterally to the left. Thus, in our case, the neglect of the left image is equivalent to a right monocular functional blindness. However, bell cancellation test clearly worsened when assessed in left monocular vision confirming that eye patching can worsen attentional visual neglect. In conclusion, our case argues for the possibility of a functional monocular blindness induced by visual neglect. We think that in presence of strabismus, absence of diplopia should induce the search for hemispatial visual neglect when supratentorial lesions are suspected.     

What determines sustained visual attention? The impact of distracter positions, task difficulty and visual fields compared

We quantified the interference of distracter stimuli on sustained visuo-spatial attention as a function of the distribution of attended positions in the visual fields (bilateral/unilateral, left/right, upper/lower), distracter positions (peripheral, between attended positions, between fixation and attended positions) and task difficulty. Compared to distinct distracter positions, bilateral field and lower field presentation had much stronger influence on the performance. Additionally, interactive effects between task difficulty and distracter position were found. This result was at variance with the previous models of visuo-spatial attention, which attached much more importance to the role of distracter positions compared to visual field effects. In directly comparing the impact of the abovementioned factors, the converse finding is evident-visual field effects, in particular bilateral presentations have a much stronger importance. Moreover, metaphoric concepts of attention like the "zoom lens" are not compatible with these results. The findings are discussed in the light of alternative models of sustained visuo-spatial attention. The visual system architecture and top-down mechanisms are considered.     

Correction to: Multimodal visual system analysis as a biomarker of visual hallucinations in Parkinson’s disease

Journal of Neurology -     

Do neck-proprioceptive and caloric-vestibular stimulation influence covert visual attention in normals, as they influence visual neglect?

Neck-proprioceptive and caloric-vestibular stimulation have been shown to ameliorate the spatial bias exhibited by patients suffering from unilateral visual neglect. These interventions might in principle have their effect by biasing covert attention towards the neglected side. If so, the same interventions should also modulate covert attention in neurologically-intact subjects. However, we demonstrate here that neither neck-proprioception (vibration of left neck muscles) nor caloric-vestibular stimulation (injection of iced water into the left ear) affect covert visual attention in healthy individuals. These results from normals may distinguish between different accounts for unilateral neglect in patients. In particular, they argue against explanations of neglect solely in terms of a pathological misperception of body orientation within an otherwise normal neural representation of space.     

Can persons with schizophrenia appreciate visual art?

The way schizophrenia patients perceive the world is largely mysterious. Understanding and appreciating the visual world begins with the perception of basic visual features, which is altered in this mental disorder. Yet, the roles basic visual features play in functional activities such as appreciation of art are unclear. This study examined the effects of visual feature manipulation on beauty perception of art in schizophrenia patients (n=29) and in normal controls (n=30). Three pieces of art--The Starry Night (Van Gogh), Mona Lisa (Da Vinci) and a natural landscape photograph (anonymous)--were manipulated in terms of their coloration (removal of color), spatial frequency content (low or high-frequency pass) and visual noise level (with added noise). Subjects judged the beauty of the original and visual-feature-manipulated artworks by rating each piece individually (1 to 7) and by ranking all pieces from most to least beautiful. For the three original art pieces, averaged ratings and rankings were similar in patients and controls. However, when the visual features of the original pieces were manipulated, changes in the beauty ratings were significantly smaller in patients. The reduced sensitivity to visual feature manipulations suggests that the modulation of basic visual signals, often used for vivid and dynamic expressions in art, may be under-appreciated in schizophrenia.     

Are neural correlates of visual consciousness retinotopic?

Some visual neurons code what we see, their defining characteristic being a response profile which mirrors conscious percepts rather than veridical sensory attributes. One issue yet to be resolved is whether, within a given cortical area, conscious visual perception relates to diffuse activity across the entire population of such cells or focal activity within the sub-population mapping the location of the perceived stimulus. Here we investigate the issue in the human brain with fMRI, using a threshold stimulation technique to dissociate perceptual from non-perceptual activity. Our results point to a retinotopic organisation of perceptual activity in early visual areas, with independent perceptual activations for different regions of visual space.     

Visual memory testing in older adults with age-related visual decline: a measure of memory performance or visual functioning?

Although we know that vision is correlated with memory performance in older adults, the implications for this in terms of neuropsychological assessment have not been investigated. Relationships among age, visual acuity, and visual and verbal memory in 89 community dwelling volunteers aged 60 to 87 years were examined. Vision was tested using the Landolt C and visual and verbal memory were assessed via the Visual Reproduction (VR) and Word List (WL) subtests from the Wechsler Memory Scale, Third Edition (WMS-III; Wechsler, 1997), respectively. Significant correlations were observed between vision and the VR and WL tasks. Hierarchical multiple regression analyses revealed that vision significantly increased the R2 for VR and WL after controlling for age and education. The effect of vision was not specific to visual memory. We conclude that vision is correlated with general memory function in older adults, and is not modality specific.     

Detection of visual change: mismatch or rareness?

How do we detect changes in our visual environment? By continuously comparing visual inputs to templates of experiences in the immediate past? Or by determining their rareness, how infrequently a visual event occurred previously? Recent results from event-related potentials have been interpreted in favour of the first hypothesis, as in the case of the auditory mismatch negativity. Here we demonstrate that rareness, rather than mismatch with a template, underlies visual change detection. Such rareness is detected through a dedicated mechanism in human visual cortex about 100 ms after the rare event occurs, reflected in the rareness-related negativity (RRN).     

The anterior ectosylvian visual area of the ferret: a homologue for an enigmatic visual cortical area of the cat?

The present paper describes the results of electrophysiological mapping experiments focused on the anterior limb of the ectosylvian gyrus of the ferret (Mustela putorius). The aim was to determine if the ferret possessed a homologous cortical area to the anterior ectosylvian visual area (AEV) of the domestic cat, but not clearly delineated in any other mammal studied to date. We were able to gather data on the visuotopic organization of a region that we consider to be a homologue of cat AEV. The visual map in this area showed a distinct visuotopic organization and covered a large extent of the visual field. Within the ferret AEV there were clusters of bimodal recording sites (somato-visual and audio-visual) that were located adjacent to surrounding unimodal cortical areas (such as the second somatosensory area and primary and secondary auditory areas). The ferret AEV, like that of the cat, was topographically isolated from other visual cortical areas by intervening auditory and somatosensory areas. Taken together these features suggest that the region described here as AEV in the ferret is indeed a direct homologue of the previously described cat AEV.     

How are visual words represented? Insights from EEG‐based visual word decoding,feature derivation and image reconstruction

Investigations into the neural basis of reading have shed light on the cortical locus and the functional role of visual‐orthographic processing. Yet, the fine‐grained structure of neural representations subserving reading remains to be clarified. Here, we capitalize on the spatiotemporal structure of electroencephalography (EEG) data to examine if and how EEG patterns can serve to decode and reconstruct the internal representation of visually presented words in healthy adults. Our results show that word classification and image reconstruction were accurate well above chance, that their temporal profile exhibited an early onset, soon after 100 ms, and peaked around 170 ms. Further, reconstruction results were well explained by a combination of visual‐orthographic word properties. Last, systematic individual differences were detected in orthographic representations across participants. Collectively, our results establish the feasibility of EEG‐based word decoding and image reconstruction. More generally, they help to elucidate the specific features, dynamics, and neurocomputational principles underlying word recognition.     

What do catastrophic visual binding failures look like?

Ordinary vision is considered a binding success: all the pieces and aspects of an image are bound together, despite being processed by many different neurons in several different cortical areas. How this is accomplished is a key problem in visual neuroscience. The study of visual binding might be facilitated if we had ways to induce binding failures. A particularly interesting failure would involve a loss of the physical integrity of the image. Here, we identify conditions that induce such perceptual failures (e.g. the melting together of equiluminant colored images and the fragmentation of retinally stabilized images) and we suggest that these should studied using electrophysiological measures of binding.     

Are Alzheimer's disease patients able to learn visual prototypes?

Recently, controversial results emerged regarding visual prototype learning in Alzheimer's disease (AD). The aim of this study was to elucidate this issue in a larger population of AD patients. The AD patients (N=72) and age-matched healthy control subjects (N=25) learned to recognize and to categorize visual dot patterns. In comparison with the control subjects, the AD patients as a group showed dysfunctions in the recognition task, whereas categorization was relatively spared in their case. Recognition was impaired in patients with mild AD (Mini-Mental score: 18-23) and moderate AD (Mini-Mental score<18), whereas categorization was impaired only in patients with moderate AD. These results suggest that while the medio-temporal/diencephalic explicit memory system is markedly affected even in early AD, the sensory neocortical areas mediating implicit category learning display a sufficient degree of functional capacity until later stages of the disease.