MyMedR

Displaying all 4 publications

Abstract:

Sort:

Collinear facilitation and contour integration in autistic adults: Examining lateral and feedback connectivity

Gowen E, Jachim S, Subri S, Dickinson C, Hamblin-Pyke B, Warren PA

Vision Res, 2020 12;177:56-67.
PMID: 32977182 DOI: 10.1016/j.visres.2020.08.004

Alongside difficulties with communication and social interaction, autism is often accompanied by unusual sensory and perceptual experiences including enhanced visual performance on tasks that involve separating local parts from global context. This superiority may be the result of atypical integrative processing, involving feedback and lateral connections between visual neurons. The current study investigated the integrity of these connections in autistic adults by examining two psychophysics tasks that rely on these processes - collinear facilitation and contour integration. The relative contribution of feedback and lateral connectivity was studied by altering the timing of the target relative to the flankers in the collinear facilitation task, in 16 autistic and 16 non-autistic adults. There were no significant differences in facilitation between the autistic and non-autistic groups, indicating that for this task and participant sample, lateral and feedback connectivity appear relatively intact in autistic individuals. Contour integration was examined in a different group of 20 autistic and 18 non-autistic individuals, for open and closed contours to assess the closure effect (improved detection of closed compared to open contours). Autistic individuals showed a reduced closure effect at both short (150 ms) and longer (500 ms) stimulus presentation durations that was driven by better performance of the autistic group for the open contours. These results suggest that reduced closure in a simple contour detection paradigm is unlikely to be due to slower global processing. Reduced closure has implications for understanding sensory overload by contributing to reduced figure-ground segregation of salient visual features.

Matched MeSH terms: Psychophysics
Fulltext Psychophysical and physiological study of asymmetric lifting and lowering task for Malaysian males

Mirta Widia, Siti Zawiah Md Dawal, NukmanYusoff

Malaysian Journal of Public Health Medicine, 2016;16(20):99-105.
MyJurnal

Extensive research has been carried out over the years to determine the maximum acceptable weight that a worker is capable of lifting in a given situation among the Occidental populations in the Europe and US. At present, there is a scarcity of studies in which lifting frequency is used as the measuring variable, especially in developing countries such as Malaysia. Therefore, the objective of this study is to determine the effects of lifting loads on the maximum acceptable frequency limit (MAFL), physiological response (muscle activity) and rating of perceived exertion (RPE) for asymmetric lifting and lowering tasks of Malaysian males.Ten male subjects are recruited in this study and they perform asymmetric lifting and lowering tasks repetitively for 30 minutes. Two lifting loads are considered (1) 1 kg and (2) 5 kg. Each of the subjects adjusts his frequency of lifting using a psychophysical approach. The subjects are instructed to perform the lifting and lowering task as fast as they could over duration of 30 minutes without exhausting themselves or becoming overheated. Electromyography (EMG) signals are recorded from four muscles (Right Erector Spinae (RES), Left Erector Spinae (LES), Right Trapezius p Descendenz (RTD) and Left Trapezius p Descendenz (LTD) and analysed in terms of the normalized MVC during asymmetric lifting and lowering tasks. The ratings of perceived exertion (RPE) for four body parts (arms, lower back, shoulders and entire body) are also collected after the subjects have completed the lifting and lowering task. The mean frequency of the lifting and lowering task obtained from the experiment is 13.41 and 9.66 times/minute for a lifting load of 1 and 5 kg, respectively. The results of the independent sample t-test show that load has a statistically significant effect on the maximum acceptable frequency limit (p < 0.05). However, it is found that even though there is an increase in muscle activity and RPE with an increase in lifting load, there is no significant difference in the overall mean muscle activity and RPE (p > 0.05). The percentage decrease in the maximum acceptable frequency for Malaysian males is higher than the Occidental populations for both of the loads investigated in this study.

Matched MeSH terms: Psychophysics
Spectral sensitivity in patients with dysthyroid eye disease

Sharanjeet-Kaur, Dickinson CM, O'Donoghue E, Murray IJ

Ophthalmic Physiol Opt, 1997 May;17(3):232-8.
PMID: 9196665 DOI: 10.1111/j.1475-1313.1997.0_749.x

The majority of patients with dysthyroid eye disease have an acquired colour vision defect. However, no psychophysical investigation of selective damage to colour or flicker pathways has been carried out. In order to clarify the nature of the visual pathology, we have used a psychophysical technique (spectral sensitivity) to selectively stimulate the chromatic and achromatic mechanisms. Spectral spots of size 1 degree presented at a rate of 1 Hz on a bright 1000 td white background are detected by the chromatic mechanism but a rate of 25 Hz reveals the achromatic mechanism. Fifteen patients (28 eyes) between the ages of 50-70 years were tested. The study showed that all patients had reduced spectral sensitivity, either 1 Hz, 25 Hz or both. The patients with reduced 1 Hz or 25 Hz spectral sensitivity only had a shorter systemic and ocular duration of the condition, had no proptosis, normal intraocular pressures in primary gaze, slightly higher intraocular pressures on upgaze, normal visual field plots and FM 100-Hue error scores higher than the normal age-matched values. The patients with reduced both 1 Hz and 25 Hz spectral sensitivities had a longer systemic and ocular duration of the condition, had proptosis, normal intraocular pressures in primary position, higher intraocular pressures on upgaze and higher FM 100-Hue error scores than the age-matched normals and those in Groups 1 and 2. A total of 50% of patients in Group 3 had defective visual field plots. These data suggest that there is a damage of the large achromatic fibres and small chromatic fibres in dysthyroid eye disease. The mechanism of the damage could be one of ischaemic or mechanical or both.

Matched MeSH terms: Psychophysics
Insights for mfVEPs from perimetry using large spatial frequency-doubling and near frequency-doubling stimuli in glaucoma

Abdullah SN, Sanderson GF, Husni MA, Maddess T

Documenta ophthalmologica. Advances in ophthalmology, 2020 08;141(1):45-55.
PMID: 32034583 DOI: 10.1007/s10633-020-09750-7

PURPOSE: To compare two forms of perimetry that use large contrast-modulated grating stimuli in terms of: their relative diagnostic power, their independent diagnostic information about glaucoma and their utility for mfVEPs. We evaluated a contrast-threshold mfVEP in normal controls using the same stimuli as one of the tests.
METHODS: We measured psychophysical contrast thresholds in one eye of 16 control subjects and 19 patients aged 67.8 ± 5.65 and 71.9 ± 7.15, respectively, (mean ± SD). Patients ranged in disease severity from suspects to severe glaucoma. We used the 17-region FDT-perimeter C20-threshold program and a custom 9-region test (R9) with similar visual field coverage. The R9 stimuli scaled their spatial frequencies with eccentricity and were modulated at lower temporal frequencies than C20 and thus did not display a clear spatial frequency-doubling (FD) appearance. Based on the overlapping areas of the stimuli, we transformed the C20 results to 9 measures for direct comparison with R9. We also compared mfVEP-based and psychophysical contrast thresholds in 26 younger (26.6 ± 7.3 y, mean ± SD) and 20 older normal control subjects (66.5 ± 7.3 y) control subjects using the R9 stimuli.
RESULTS: The best intraclass correlations between R9/C20 thresholds were for the central and outer regions: 0.82 ± 0.05 (mean ± SD, p ≤ 0.0001). The areas under receiver operator characteristic plots for C20 and R9 were as high as 0.99 ± 0.012 (mean ± SE). Canonical correlation analysis (CCA) showed significant correlation (r = 0.638, p = 0.029) with 1 dimension of the C20 and R9 data, suggesting that the lower and higher temporal frequency tests probed the same neural mechanism(s). Low signal quality made the contrast-threshold mfVEPs non-viable. The resulting mfVEP thresholds were limited by noise to artificially high contrasts, which unlike the psychophysical versions, were not correlated with age.
CONCLUSION: The lower temporal frequency R9 stimuli had similar diagnostic power to the FDT-C20 stimuli. CCA indicated the both stimuli drove similar neural mechanisms, possibly suggesting no advantage of FD stimuli for mfVEPs. Given that the contrast-threshold mfVEPs were non-viable, we used the present and published results to make recommendations for future mfVEP tests.

Matched MeSH terms: Psychophysics