Retinal thickness in Parkinson's disease

BACKGROUND: Visual symptoms are common in Parkinson's disease with studies consistently demonstrating reductions in visual acuity, contrast sensitivity, colour and motion perception as well as alterations in electroretinogram latencies and amplitudes. Optical coherence tomography can examine retinal structure non-invasively and retinal thinning has been suggested as a potential biomarker for neurodegeneration in Parkinson's disease. Our aim was to examine the retinal thickness of a cohort of Parkinson's disease subjects (and age-matched controls) to establish the practical utility of optical coherence tomography in a representative older Parkinson's disease group. METHODS: Fifty-one established Parkinson's disease subjects and 25 healthy controls were subjected to ophthalmological assessment and optical coherence tomography (Zeiss Stratus 3000™) of macular thickness and volume and retinal nerve fibre thickness around the optic nerve head. Twenty four percent of control and 20% of Parkinson's disease subjects were excluded from final analysis due to co-morbid ocular pathology. Further data was excluded either due to poor tolerability of optical coherence tomography or poor quality scans. RESULTS: Despite a reduction in both visual acuity and contrast sensitivity in the residual evaluable Parkinson's disease cohort, we did not detect any differences between the two study groups for any measures of retinal thickness, in contrast to previously published work. CONCLUSIONS: In addition to technical problems inherent in the evaluation, the lack of difference between Parkinson's disease and healthy control subjects suggests longitudinal studies, employing newer techniques, will be required to define the role of optical coherence tomography as a potential diagnostic biomarker.

Reduced perception of the motion-induced blindness illusion in schizophrenia

Motion-induced blindness (MIB) occurs when target stimuli are presented together with a moving distractor pattern. Most observers experience the targets disappearing and reappearing repeatedly for periods of up to several seconds. MIB can be viewed as a striking marker for the organization of cognitive functioning. In the present study, MIB rates and durations were assessed in 34 schizophrenia-spectrum disorder patients and matched controls. The results showed that positive symptoms and excitement enhanced MIB, whereas depression and negative symptoms attenuated the illusion. MIB was more frequently found in normal subjects. The results remained consistent after adjusting for reaction time and error rates. Hence, MIB may provide a valid and reliable measure of cognitive organization in schizophrenia.

Altered perception of apparent motion in schizophrenia spectrum disorder

Apparent motion (AM), the Gestalt perception of motion in the absence of physical motion, was used to study perceptual organization and neurocognitive binding in schizophrenia. Associations between AM perception and psychopathology as well as meaningful subgroups were sought. Circular and stroboscopic AM stimuli were presented to 68 schizophrenia spectrum patients and healthy participants. Psychopathology was measured using the Positive and Negative Syndrome Scale (PANSS). Psychopathology was related to AM perception differentially: Positive and disorganization symptoms were linked to reduced gestalt stability; negative symptoms, excitement and depression had opposite regression weights. Dimensions of psychopathology thus have opposing effects on gestalt perception. It was generally found that AM perception was closely associated with psychopathology. No difference existed between patients and controls, but two latent classes were found. Class A members who had low levels of AM stability made up the majority of inpatients and control subjects; such participants were generally young and male, with short reaction times. Class B typically contained outpatients and some control subjects; participants in class B were older and showed longer reaction times. Hence AM perceptual dysfunctions are not specific for schizophrenia, yet AM may be a promising stage marker.

Development of a novel fMRI compatible visual perception prototype battery to test older people with and without dementia

Background: Visuoperceptual deficits in dementia are common and can reduce quality of life. Testing of visuoperceptual function is often confounded by impairments in other cognitive domains and motor dysfunction. We aimed to develop, pilot, and test a novel visuocognitive prototype test battery which addressed these issues, suitable for both clinical and functional imaging use. Methods: We recruited 23 participants (14 with dementia, 6 of whom had extrapyramidal motor features, and 9 age-matched controls). The novel Newcastle visual perception prototype battery (NEVIP-B-Prototype) included angle, color, face, motion and form perception tasks, and an adapted response system. It allows for individualized task difficulties. Participants were tested outside and inside the 3T functional magnetic resonance imaging (fMRI) scanner. Functional magnetic resonance imaging data were analyzed using SPM8. Results: All participants successfully completed the task inside and outside the scanner. Functional magnetic resonance imaging analysis showed activation regions corresponding well to the regional specializations of the visual association cortex. In both groups, there was significant activity in the ventral occipital-temporal region in the face and color tasks, whereas the motion task activated the V5 region. In the control group, the angle task activated the occipitoparietal cortex. Patients and controls showed similar levels of activation, except on the angle task for which occipitoparietal activation was lower in patients than controls. Conclusion: Distinct visuoperceptual functions can be tested in patients with dementia and extrapyramidal motor features when tests use individualized thresholds, adapted tasks, and specialized response systems.

Interhemispheric connections shape subjective experience of bistable motion

The right and left visual hemifields are represented in different cerebral hemispheres and are bound together by connections through the corpus callosum. Much has been learned on the functions of these connections from split-brain patients [1-4], but little is known about their contribution to conscious visual perception in healthy humans. We used diffusion tensor imaging and functional magnetic resonance imaging to investigate which callosal connections contribute to the subjective experience of a visual motion stimulus that requires interhemispheric integration. The "motion quartet" is an ambiguous version of apparent motion that leads to perceptions of either horizontal or vertical motion [5]. Interestingly, observers are more likely to perceive vertical than horizontal motion when the stimulus is presented centrally in the visual field [6]. This asymmetry has been attributed to the fact that, with central fixation, perception of horizontal motion requires integration across hemispheres whereas perception of vertical motion requires only intrahemispheric processing [7]. We are able to show that the microstructure of individually tracked callosal segments connecting motion-sensitive areas of the human MT/V5 complex (hMT/V5+; [8]) can predict the conscious perception of observers. Neither connections between primary visual cortex (V1) nor other surrounding callosal regions exhibit a similar relationship.

EEG signs of vigilance fluctuations preceding perceptual flips in multistable illusionary motion

This EEG study was performed to clarify the time course of brain electrical events and possible vigilance changes associated with perceptual flips during multistable perception. 13 healthy subjects (28.5 3.8 years) were recorded with a 21-channel digital EEG during a stroboscopic alternative motion paradigm implying illusionary motion with ambiguous direction. Perceptual flips were preceded by a significant decrease of EEG frequencies, and followed by a significant frequency increase with a trend to overshoot. EEG slowing is a reliable sign of vigilance decrease and can be related to thalamic deactivation. This is consistent with a recent fMRI study, which showed thalamic deactivation associated with perceptual flips. The study added important chronological information about this phenomenon and allows the conclusion that reduced vigilance facilitates perceptual discontinuities during multistable perception.

Visual perception in Parkinson disease dementia and dementia with Lewy bodies

OBJECTIVE To quantify visual discrimination, space-motion, and object-form perception in patients with Parkinson disease dementia (PDD), dementia with Lewy bodies (DLB), and Alzheimer disease (AD). METHODS The authors used a cross-sectional study to compare three demented groups matched for overall dementia severity (PDD: n = 24; DLB: n = 20; AD: n = 23) and two age-, sex-, and education-matched control groups (PD: n = 24, normal controls [NC]: n = 25). RESULTS Visual perception was globally more impaired in PDD than in nondemented controls (NC, PD), but was not different from DLB. Compared to AD, PDD patients tended to perform worse in all perceptual scores. Visual perception of patients with PDD/DLB and visual hallucinations was significantly worse than in patients without hallucinations. CONCLUSIONS Parkinson disease dementia (PDD) is associated with profound visuoperceptual impairments similar to dementia with Lewy bodies (DLB) but different from Alzheimer disease. These findings are consistent with previous neuroimaging studies reporting hypoactivity in cortical areas involved in visual processing in PDD and DLB.

A Hierarchical Bayesian Model for Measuring Motion Adaptation

Previous research has shown that motion imagery draws on the same neural circuits that are involved in perception of motion, thus leading to a motion aftereffect (Winawer et al., 2010). Imagined stimuli can induce a similar shift in participants’ psychometric functions as neural adaptation due to a perceived stimulus. However, these studies have been criticized on the grounds that they fail to exclude the possibility that the subjects might have guessed the experimental hypothesis, and behaved accordingly (Morgan et al., 2012). In particular, the authors claim that participants can adopt arbitrary response criteria, which results in similar changes of the central tendency μ of psychometric curves as those shown by Winawer et al. (2010).

Psychological Data from an Exploration of the Rapport / Synchrony Interplay Using Motion Energy Analysis

These data result from an investigation examining the interplay between dyadic rapport and consequential behavior-mirroring. Participants responded to a variety of interpersonally-focused pretest measures prior to their engagement in videotaped interdependent tasks (coded for interactional synchrony using Motion Energy Analysis [17,18]). A post-task evaluation of rapport and other related constructs followed each exchange. Four studies shared these same dependent measures, but asked distinct questions: Study 1 (Ndyad = 38) explored the influence of perceived responsibility and gender-specificity of the task; Study 2 (Ndyad = 51) focused on dyad sex-makeup; Studies 3 (Ndyad = 41) and 4 (Ndyad = 63) examined cognitive load impacts on the interactions. Versions of the data are structured with both individual and dyad as the unit of analysis. Our data possess strong reuse potential for theorists interested in dyadic processes and are especially pertinent to questions about dyad agreement and interpersonal perception / behavior association relationships.

Whole-body motion discrimination in the visually impaired

Visually impaired people show superior abilities in various perception tasks such as auditory attention, auditory temporal resolution, auditory spatial tuning, and odor discrimination. However, with the use of psychophysical methods, auditory and olfactory detection thresholds typically do not differ between visually impaired and sighted participants. Using a motion platform we investigated thresholds of passive whole-body motion discrimination in nine visually impaired participants and nine age-matched sighted controls. Participants were rotated in yaw, tilted in roll, and translated along the y-axis at two different frequencies (0.3 Hz and 2 Hz). An adaptive 3-down 1-up staircase procedure was used along with a two-alternative direction (leftward vs. rightward) discrimination task. Superior performance of visually impaired participants was found in the 0.3 Hz roll tilt condition. No differences between the visually impaired and controls were observed in all other types of motion. The superior performance in the 0.3 Hz roll tilt condition could reflect differences in the integration of extra-vestibular cues and increased sensitivity towards changes in the direction of the gravito-inertial force. In the absence of visual information, roll tilts entail a more pronounced risk of falling, and this could eventually account for the group difference. It is argued that differences in experimental procedures (i.e. detection vs. discrimination of stimuli) explain the discrepant findings across perceptual tasks comparing blind and sighted participants.

Impairments of peripheral motion change detection during smooth pursuit eye movements

Introduction: In team sports the ability to use peripheral vision is essential to track a number of players and the ball. By using eye-tracking devices it was found that players either use fixations and saccades to process information on the pitch or use smooth pursuit eye movements (SPEM) to keep track of single objects (Schütz, Braun, & Gegenfurtner, 2011). However, it is assumed that peripheral vision can be used best when the gaze is stable while it is unknown whether motion changes can be equally well detected when SPEM are used especially because contrast sensitivity is reduced during SPEM (Schütz, Delipetkose, Braun, Kerzel, & Gegenfurtner, 2007). Therefore, peripheral motion change detection will be examined by contrasting a fixation condition with a SPEM condition. Methods: 13 participants (7 male, 6 female) were presented with a visual display consisting of 15 white and 1 red square. Participants were instructed to follow the red square with their eyes and press a button as soon as a white square begins to move. White square movements occurred either when the red square was still (fixation condition) or moving in a circular manner with 6 °/s (pursuit condition). The to-be-detected white square movements varied in eccentricity (4 °, 8 °, 16 °) and speed (1 °/s, 2 °/s, 4 °/s) while movement time of white squares was constant at 500 ms. 180 events should be detected in total. A Vicon-integrated eye-tracking system and a button press (1000 Hz) was used to control for eye-movements and measure detection rates and response times. Response times (ms) and missed detections (%) were measured as dependent variables and analysed with a 2 (manipulation) x 3 (eccentricity) x 3 (speed) ANOVA with repeated measures on all factors. Results: Significant response time effects were found for manipulation, F(1,12) = 224.31, p < .01, ηp2 = .95, eccentricity, F(2,24) = 56.43; p < .01, ηp2 = .83, and the interaction between the two factors, F(2,24) = 64.43; p < .01, ηp2 = .84. Response times increased as a function of eccentricity for SPEM only and were overall higher than in the fixation condition. Results further showed missed events effects for manipulation, F(1,12) = 37.14; p < .01, ηp2 = .76, eccentricity, F(2,24) = 44.90; p < .01, ηp2 = .79, the interaction between the two factors, F(2,24) = 39.52; p < .01, ηp2 = .77 and the three-way interaction manipulation x eccentricity x speed, F(2,24) = 3.01; p = .03, ηp2 = .20. While less than 2% of events were missed on average in the fixation condition as well as at 4° and 8° eccentricity in the SPEM condition, missed events increased for SPEM at 16 ° eccentricity with significantly more missed events in the 4 °/s speed condition (1 °/s: M = 34.69, SD = 20.52; 2 °/s: M = 33.34, SD = 19.40; 4 °/s: M = 39.67, SD = 19.40). Discussion: It could be shown that using SPEM impairs the ability to detect peripheral motion changes at the far periphery and that fixations not only help to detect these motion changes but also to respond faster. Due to high temporal constraints especially in team sports like soccer or basketball, fast reaction are necessary for successful anticipation and decision making. Thus, it is advised to anchor gaze at a specific location if peripheral changes (e.g. movements of other players) that require a motor response have to be detected. In contrast, SPEM should only be used if a single object, like the ball in cricket or baseball, is necessary for a successful motor response. References: Schütz, A. C., Braun, D. I., & Gegenfurtner, K. R. (2011). Eye movements and perception: A selective review. Journal of Vision, 11, 1-30. Schütz, A. C., Delipetkose, E., Braun, D. I., Kerzel, D., & Gegenfurtner, K. R. (2007). Temporal contrast sensitivity during smooth pursuit eye movements. Journal of Vision, 7, 1-15.