Glaucoma-associated abnormalities in cortical activity during a visuocognitive task.

OBJECTIVE: To investigate neurophysiological dynamics during a visuocognitive task in glaucoma patients vs. healthy controls. METHODS: Fifteen patients with early-stage primary open-angle glaucoma (POAG) and fifteen age-matched healthy participants underwent a "go/no-go" task, monitored with EEG. Participants had to semantically categorize visual objects in central vision, with animal or furniture as targets according to the experimental block. RESULTS: Early visual processing was delayed by 50 ms in patients with POAG compared to controls. The patients displayed a smaller difference between animal and furniture categorization during higher-level cognitive processing (at 400-600 ms). Regarding behavioral data, the groups differed in accuracy performance and decision criterion. As opposed to the control group, patients did not display facilitation and a higher accuracy rate for animal stimuli. However, patients maintained a consistent decision criterion throughout the experiment, whereas controls displayed a shift towards worse decision criteria in furniture trials, with higher error rate. CONCLUSIONS: The comparative analysis of behavioral and neurophysiological data revealed in POAG patients a delay in early visual processing, and potential high-level cognitive compensation during late, task-dependent activations. SIGNIFICANCE: To our knowledge, our findings provide the first evidence of modification in cognitive brain dynamics associated with POAG.

Central Visual Attention in Primary Open-angle Glaucoma.

SIGNIFICANCE: To better understand the implication of a potential cognitive change in glaucoma, patients were stimulated in central visual areas considered functionally normal to discard an effect due to the loss of vision during an attentional task. The outcome might improve the follow-up on the impact of the pathology. PURPOSE: This study aimed to evaluate the effect of primary open-angle glaucoma on the visual attention system by recording responses of behavioral and oculomotor strategies. METHODS: We included 20 individuals with primary open-angle glaucoma (62.1 ± 7.2 years old), 18 age-matched control subjects (58.4 ± 7.2 years old), and 20 young control subjects (25.7 ± 3.5 years old). The procedure consisted of visual (eye-tracking recordings) and manual detection of a target. All participants had to detect a square with a vertical bar within distractors (squares, triangles, and circles with a horizontal or vertical bar) of identical size of 1.6 × 1.6° visual angle. The shapes were displayed concentrically on a radius of 5° of visual angle. All participants were tested to ensure that their visual field sensitivity was normal within ±5° central vision. RESULTS: In responding manually, glaucoma participants were slower than age-matched control subjects (1723 ± 488 vs. 1263 ± 385 milliseconds; P < .01). Eye-tracking recordings showed that glaucoma participants found the target within the same time frame as age-matched control subjects. Compared with the young group, the scanpath length and average fixation duration on distractors were significantly longer for the glaucoma patients (+235 pixels, +104 milliseconds) and the age-matched control participants (+120 pixels, +39 milliseconds). Impaired contrast sensitivity was correlated with longer response time, longer scanpath, and longer fixation on distractors. CONCLUSIONS: Glaucoma affects the manual response times in a visual attention task, but patients can visually detect the target as quickly as age-matched control subjects. Different clinical factors predicted the performances. The age of the patients was associated with longer scanpath. The visual field loss (mean deviation) was linked with longer visual response time. The loss of contrast sensitivity predicted the behavioral change on fixation duration to the distractors, global response time, visual response time, and scanpath length.

Dynamics of low-pass-filtered object categories: A decoding approach to ERP recordings.

Rapid analysis of low spatial frequencies (LSFs) in the brain conveys the global shape of the object and allows for rapid expectations about the visual input. Evidence has suggested that LSF processing differs as a function of the semantic category to identify. The present study sought to specify the neural dynamics of the LSF contribution to the rapid object representation of living versus non-living objects. In this EEG experiment, participants had to categorize an object displayed at different spatial frequencies (LSF or non-filtered). Behavioral results showed an advantage for living versus non-living objects and a decrease in performance with LSF pictures of pieces of furniture only. Moreover, despite a difference in classification performance between LSF and non-filtered pictures for living items, the behavioral performance was maintained, which suggests that classification under our specific condition can be based on LSF information, in particular for living items.

The nature of blindsight: implications for current theories of consciousness.

Blindsight regroups the different manifestations of preserved discriminatory visual capacities following the damage to the primary visual cortex. Blindsight types differentially impact objective and subjective perception, patients can report having no visual awareness whilst their behaviour suggests visual processing still occurs at some cortical level. This phenomenon hence presents a unique opportunity to study consciousness and perceptual consciousness, and for this reason, it has had an historical importance for the development of this field of research. From these studies, two main opposing models of the underlying mechanisms have been established: (a) blindsight is perception without consciousness or (b) blindsight is in fact degraded vision, two views that mirror more general theoretical options about whether unconscious cognition truly exists or whether it is only a degraded form of conscious processing. In this article, we want to re-examine this debate in the light of recent advances in the characterization of blindsight and associated phenomena. We first provide an in-depth definition of blindsight and its subtypes, mainly blindsight type I, blindsight type II and the more recently described blindsense. We emphasize the necessity of sensitive and robust methodology to uncover the dissociations between perception and awareness that can be observed in brain-damaged patients with visual field defects at different cognitive levels. We discuss these different profiles of dissociation in the light of both contending models. We propose that the different types of dissociations reveal a pattern of relationship between perception, awareness and metacognition that is actually richer than what is proposed by either of the existing models. Finally, we consider this in the framework of current theories of consciousness and touch on the implications the findings of blindsight have on these.

Glaucoma and Computer Use: Do Contrast and Color Enhancements Improve Visual Comfort in Patients?

PURPOSE: To estimate the impact of glaucoma on computer use and to assess specific adaptations of the graphical interface to this form of visual impairment. DESIGN: Prospective, experimental cohort study. PARTICIPANTS: Forty-nine participants were recruited: 16 patients with primary open-angle glaucoma (mean ± SD, 62.7 ± 5.6 years of age), 17 age-matched participants (mean ± SD, 59.1 ± 8.3 years of age), and 16 young control participants (mean ± SD, 23.3 ± 2.1 years of age). METHODS: An ophthalmologic examination before the study evaluated the level of visual loss (mean deviation), visual acuity (logarithm of the minimum angle of resolution units), and contrast sensitivity (CS) of the primary open-angle glaucoma patients. Each participant underwent the following measurements: an information technology (IT) experience questionnaire, a preference task monitored by eye tracking, and a feedback session. The experimental task was based on ecological computer scenes with 3 enhancement levels (low, medium, and high), determined by gradual modulation of contrast, luminance, and color. Participants were asked to select the most readable and comfortable stimulus among 4 images displayed on the screen: the original computer scene and 3 enhanced versions. MAIN OUTCOME MEASURES: Clinical, oculomotor, and subjective data were computed together in a multivariate model by using a principal component analysis (PCA). RESULTS: The PCA revealed 3 principal components accounting for 72% of the total variance of the data and showed a greater need for enhanced computer scenes in glaucoma patients, an equal preference for low and medium enhancement within the 3 groups, and significantly longer oculomotor behavior in the patient groups. Subjective reports of difficulty using IT because of vision were correlated with visual impairment and high enhancement preference. Contrast sensitivity was critical to explaining the main variations of the data. A reduced CS had a significant effect on the preference for enhanced computer scenes (r = -0.43; P < 0.002) and a less effective exploration velocity (r = 0.43; P < 0.002). CONCLUSIONS: Glaucoma alters the global exploration of computer scenes. High enhancement of the graphical interface could improve visual comfort during computer use. Subjective patients' reports underline the importance of including IT questions in visual-related quality-of-life questionnaires.

Making sense of blindsense: a reply to Phillips.

We recently published the results of a study on the occurrence of blindsight among eight, post-stroke homonymous hemianopic (HH) patients (Garric et al., 2019), in whom we measured blindsight through forced-choice tasks and assessed perceptual experiences by a new awareness scale, the Sensation Awareness Scale (SAS). Within the cohort, we found different profiles of dissociation between objective and subjective performance. Importantly, we were able to describe several cases of a dissociation phenomenon that we named blindsense, whereby patients exhibited marked subjective sensitivity in their blind hemifield despite being unable to discriminate the different stimuli. Following publication of our article (Garric et al., 2019), Prof. Ian Phillips (Phillips, 2019) wrote a Commentary in which he questioned the methodology we used to measure and analyze objective and subjective perception in our HH patients. As opposed to our original interpretation of our results to describe the new profile of blindsense, based on a non-visual experience hypothesis (Kentridge, 2015), Prof. Phillips re-evaluated the different blindsight profiles that we identified in our study through the lens of a degraded conscious vision hypothesis (Overgaard, Fehl, Mouridsen, Bergholt, & Cleeremans, 2008). In the present response, we explain that, although we agree that dichotomous visual scales lead to highly conservative responses and mask conscious perceptual experience of patients, we still support the notion that nuanced report protocols can enable more-sensitive measurements of perceptual experiences in the hemianopic, so-called blind visual field. Furthermore, we affirm that the additional awareness-scale phenomenal levels that such protocols enable are more consistent with patients' experiences and lead patients to provide more liberal responses when describing their subjective perceptions.

Dissociations between perception and awareness in hemianopia.

The most common visual defect to follow a lesion of the retrochiasmal pathways is homonymous hemianopia (HH), whereby patients are blind to the contralesional visual field of each eye. Homonymous hemianopia has been studied in terms of its deleterious consequences on perceptual, cognitive and motor tasks as well as because it represents an interesting model of vision loss after a unilateral lesion of the occipital lobe. From a behavioral perspective, in addition to exhibiting a severe deficit in their contralesional visual field, HH patients can also exhibit dissociations between perception and awareness. Firstly, HH patients suffering from anosognosia may be unaware of their visual field defect. Secondly, HH patients can present with unconscious visual abilities in the blind hemifield, a phenomenon referred to as blindsight. Thirdly, recent reports demonstrate that HH patients can suffer from a subtle deficit in their ipsilesional visual field that they are unaware of, a condition called sightblindness (i.e. the reverse case of 'blindsight'). Finally, HH patients may also exhibit visual hallucinations in their blind field; however, such patients are not systematically aware that their perceptions are unreal. In this review, we provide an overview of the visual-field losses in HH patients after a left or right unilateral occipital lesion. Furthermore, we explore the implications of these four phenomena for models of visual processing and rehabilitation of visual field defects in HH patients. Finally, in contrast to the traditional view that HH is solely a visual-field defect, we discuss why this deficit is an interesting model for studying the dissociation between perception and awareness.

Dissociation between objective and subjective perceptual experiences in a population of hemianopic patients: A new form of blindsight?

After a post-chiasmatic lesion, some patients may retain unconscious visual function, known as blindsight, in their contralesional visual field. Despite the importance of blindsight in the study of consciousness, little is known about the nature of patients' experience in their hemianopic field. To address this knowledge gap, we measured blindsight, and assessed the perceptual experience in the contralesional visual field, of seventeen homonymous hemianopic (HH) patients. To ensure that the stimuli were shown in a "blind" sector of the visual field, we selected a subgroup of eight complete-HH patients, as determined by automatic perimetry. Firstly, we measured blindsight through a forced-choice task in which the patients had to identify letters displayed on a screen. Secondly, we compared the patients' binary responses ("Something was presented" vs "Nothing was presented") to responses on a new, five-level scale, the Sensation Awareness Scale (SAS), which we designed to include visual as well as non-visual answers (e.g., "I felt something"). Interestingly, only one of the eight complete-HH patients met the criteria for blindsight. More importantly, our SAS enabled us to identify a previously unreported dissociation, which we have named blindsense, in four of the eight complete-HH patients. Specifically, these four patients exhibited better-than-chance sensitivity to the presence of a stimulus on the subjective scale, despite being unable to identify the stimulus during the forced-choice task. Our findings highlight the importance of awareness-assessment methods to investigate perceptual experiences in the contralesional visual field and suggest a low incidence of blindsight in post-stroke HH patients.