AVA Christmas Meeting (18th December, Royal Holloway University, London)

The Pint Glass Illusion: Exploring the misjudgement of curvature and length for two and three-dimensional objects

Gunnar Schmidtmann

Humans are exquisitely sensitive in curvature detection and discrimination, but misjudge the extent of curvature. A largely unexplored phenomenon is the underestimation of the circumference length of curved objects. Anecdotal, and some experimental evidence (Rivera-Aparicio & Firestone, 2018 J Vision 18(10) 1318-1318) suggests that when comparing the circumference of a Pint glass to its height, subjects significantly underestimate the circumference (Pint Glass Illusion, PGI). I present results from two experiments exploring the dependence of the PGI on segment length and type of curve for 2D and 3D shapes. (i) 10 subjects were presented with circular and elliptical arcs (2D) of varying segment length (central angle, CA = 45˚ - 360˚) and aspect ratios (AR = 1, 0.5, 0.25). Subjects adjusted a straight line to the arc length. Contrary to the PGI, results show that for all segment lengths, subjects on average overestimated the length with the largest overestimation for CA = 90˚ and 180˚ (~40%), with the most accurate estimation for the full circle and ellipses (~20%). (ii) To investigate whether results were due to the planar presentation, subjects also judged the arc length of 3D cylindroids (height 14 cm). For elliptical cylindroids with AR = 0.25 (CA = 45˚, 90˚), subjects underestimate the arc length (~ 8%). For AR = 0.5 (CA = 45˚ and 90˚), observers overestimate the arc length after which the performance is very accurate for semi and full ellipses and circles. The observed overestimation and most accurate performance for full ellipses and circles implies that the PGI might depend on different strategies, e.g. the comparison of height to circumference.

Spatial summation within static and dynamic Glass patterns

Mahesh R. Joshi, Ben J. Jennings, Gunnar Schmidtmann

Eye and Vision Research Group, University of Plymouth

Centre for Cognitive Neuroscience, College of Health, Medicine and Life Sciences, Brunel University London

Neurons in early visual cortex are tuned to local stimulus features, i.e., orientation and spatial frequency. Behaviourally, however, the stimuli that are ecologically relevant are more complex. The visual system must therefore employ mechanisms that combine these localised outputs. Previous studies addressed this question by measuring area summation for various types of Glass pattern, in which the stimulus array was divided into various sectors of increasing size. Linear summation predicts that the decrease in thresholds with increasing signal area follows a power-law function with a (log-log) slope of -1.0. This was previously found for circular Glass patterns, suggesting that the information in these patterns is linearly summed across the entire display, and was taken as evidence for specialized global detectors for circular patterns. Here we present results from summation experiments using static and dynamic Glass patterns with radial, circular, and translational structure. We measured detection thresholds as a function of signal area (25%, 50%, 100%) with the remaining area containing orientation noise. Results show that thresholds for dynamic Glass patterns were lower than for static ones across all pattern types and signal areas. In agreement with Schmidtmann et al. 2015 J Vis 15(16):6 1-19, we do not find superior sensitivities for detecting circular structure. Importantly, summation strength never reached values close to linear summation (-1) for static or dynamic patterns, implying that probability summation is the most likely basis for the detection of circular, radial, and translational Glass patterns.

New paper in Vision Research

Revealing the influence of bias in a letter acuity identification task: A noisy template model

Georgeson, M. A., Barhoom, H., Joshi, M. R., Artes, P. H., & Schmidtmann, G.

In clinical testing of visual acuity, it is often assumed that performance reflects sensory abilities and observers do not exhibit strong biases for or against specific letters, but this assumption has not been extensively tested. We re-analyzed single-letter identification data as a function of letter size, spanning the resolution threshold, for 10 Sloan letters at central and paracentral visual field locations. Individual observers showed consistent letter biases across letter sizes. Preferred letters were named much more often and others less often than expected (group averages ranged from 4% to 20% across letters, where the unbiased rate was 10%). In the framework of signal detection theory, we devised a noisy template model to distinguish biases from differences in sensitivity. When bias varied across letter templates the model fitted very well - much better than when sensitivity varied without bias. The best model combined both, having substantial biases and small variations in sensitivity across letters. The over- and under-calling decreased at larger letter sizes, but this was well-predicted by template responses that had the same additive bias for all letter sizes: with stronger inputs (larger letters) there was less opportunity for bias to influence which template gave the biggest response. The neural basis for such letter bias is not known, but a plausible candidate is the letter-recognition machinery of the left temporal lobe. Future work could assess whether such biases affect clinical measures of visual performance. Our analyses so far suggest very small effects in most settings.

Georgeson, M. A., Barhoom, H., Joshi, M. R., Artes, P. H., & Schmidtmann, G. (2023). Revealing the influence of bias in a letter acuity identification task: A noisy template model. Vision Research, 208, 108233. https://doi.org/10.1016/j.visres.2023.108233 [PDF]

Hatem is at ARVO 2023 in New Orleans

Acuity perimetry with speech input for mapping macular visual field in glaucoma

Purpose: Acuity perimetry may be more efficient compared to contrast detection in assessing macular visual field defects. We explored the use of letters as stimuli and speech as a response method to measure macular visual sensitivity in healthy observers and those with glaucoma.  

Methods: 11 eyes from 11 healthy observers and 10 eyes from 7 observers with glaucoma (macular mean deviation = -8.40 dB; SD = 5.00; M-pattern, Octopus 900, Haag-Streit, Switzerland) were examined. Letter acuity was estimated at 13 test locations within 4° from fixation (Figure 1A) using a fixed step size staircase. A speech recognition algorithm was employed as an input method to enable participants to perform the task without supervision. The observers’ perceived difficulty of the task was assessed via a questionnaire.

Results: In healthy observers, visual acuities ranged from -0.13 ± 0.03 LogMAR at fovea to 0.36± 0.05 LogMAR at 4° eccentricity (Figure 1B). In observers with glaucoma, resolution thresholds correlated closely with conventional perimetry (r between -0.48 (ST) to -0.85 (IT)). Most observers found the task easy to perform.

Conclusion: The results show that letter acuity perimetry with speech input is a feasible method to capture macular damage in glaucoma. These approaches may lead to more intuitive and patient-friendly tests for macular visual field assessments.

Download poster here

AVA Spring Meeting 2023 at the University of Plymouth (17th April)

The Spring and Annual General Meeting of the Applied Vision Association (AVA UK) will be held on Monday, 17 April 2023 at the University of Plymouth.
The aim of the meeting is to facilitate collaboration between those interested in basic and clinical vision science. 

All attendees are encouraged to submit an abstract; all aspects of vision science are welcome.

Keynote

The Geoffrey J Burton Memorial Lecture will be delivered by Prof Fiona Newell (University of Dublin, Trinity College).

Title: Cross sensory interactions influence what we see: implications for perceptual training across the lifespan

Location

The meeting will take place at the Roland Levinsky Building which is in the centre of the University of Plymouth main campus at Drake Circus, PL4 8AA. It is a short walk (approximately 0.4 miles) from Plymouth train station. A meeting-specific website has been set up and will be updated with more details closer to the meeting.

Program

Download program here

Abstracts

Download abstracts here

Registration is now open via the AVA website.

http://www.theava.net/meetings.php?s=ava-spring-meeting-2023-plymouth

New paper in Emotion

The discrimination of self from other as a component of empathy

Despite the centrality of empathy in human social life, there is no widely agreed definition or characterization of the concept of empathy. A common thread in many of the proposed definitions, however, is that empathy presupposes the discrimination of self and other on the grounds that, to empathize with another individual, the mental state of the target individual must first be distinguished from the empathizer's own mental state. The purpose of this study is to investigate this proposal empirically. We employed a paradigm in which participants rated the emotional valence and degree of arousal of 93 facial expressions of mental states. We asked participants to infer the mental state represented by each facial expression (the Other condition) as well as to describe the effect of the expression on their own mental state (the Self condition). An absolute difference score between the Other and the Self conditions was used as an index of a capacity for self-other discrimination. Empathy was measured using the Interpersonal Reactivity Index. Results show that individuals high in trait empathy discriminate between self and other to a significantly greater degree when judging mental states than individuals low in trait empathy. This suggests that the capacity for self-other discrimination may be a component of the capacity for empathy and that future investigations of the concept of empathy ought to retain it. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Little, C., Solomonova, E., Jordan, M., Klein, N., Jennings, B., Schmidtmann, G., Leos, H., & Gold, I. (2022). The discrimination of self from other as a component of empathy. Emotion. Advance online publication. https://doi.org/10.1037/emo0001193

Hatem and I attended the European Conference on Visual Perception (ECVP) 2022 in Nijmegen (28th August - 1st September).

The role of similarity and bias in letter acuity measurements: a noisy template model

Hatem Barhoom, Gunnar Schmidtmann, Mahesh R. Joshi, Paul H. Artes, Mark A. Georgeson

The poster (#59) will be presented on Thursday, 1st September, in the Peripheral Vision session at Refter in the Erasmus building.

Higher resolution version of the poster can be downloaded here.

Previous studies have demonstrated that similarity and bias are major causes of errors in the identification of Sloan letters in visual acuity testing. However, these two factors and their relative contribution have not been investigated extensively at central and paracentral visual field locations. Using the method of constant stimuli, visual acuity was measured in 10 observers at central and paracentral (±3˚ vertical meridian) visual field locations. A “noisy template” model was adapted to distinguish biases and similarities from random errors in letter identification. At all three test locations, we found that the best model was one that combined the effects of both bias and similarity. The relative contribution of bias was higher than similarity, at all three test locations. Additionally, biases may exclusively explain variations in letter identification performance for all letter sizes at the three test locations. Although there was no significant effect of bias or similarity on the estimated letter-size acuity, we observed a substantial increase in the spread of the psychometric function (mainly at the periphery and at the upper part of the psychometric function) in the models that included only similarity but not bias. . In clinical vision tests, most letter stimuli are supra-threshold, so it is plausible to attribute differences in identification performance, especially in peripheral vision, to similarity alone. However, it will be important to investigate this assumption and to examine whether bias and similarity are likely to have a clinically significant effect on measures of visual performance and letter acuity in the periphery.

PhD studentship available

The effect of mild traumatic brain injuries on visual and vestibular functions

Applications are invited for a three-year PhD studentship. The studentship will start on 1 October 2022 or later.

Project description

Patients with traumatic brain injuries (TBI) frequently suffer from a variety of visual and vestibular problems. TBI-associated visual symptoms include blurred vision, double vision, reading problems, and eye strain. In addition, many patients show vestibular symptoms, including dizziness, nausea, and impaired balance. TBI can also affect the interactions between the visual and vestibular system that preserve gaze stabilisation during self and imposed body motion resulting in visual induced dizziness. The aim of this 3-year PhD project is to systematically investigate visual and vestibular functions in TBI patients. The visual function experiments will investigate low-level (e.g., contrast sensitivity), mid-level (e.g. contour – and shape perception and high-level cortical visual processes (e.g. visual search, attention). The vestibular testing will involve a combination of clinical tests, objective oculomotor and vestibular tests and tests of visuo-vestibular interactions and eye-head coordination during visual smooth pursuit. Further, the scholar will have the opportunity to incorporate some of the neuroimaging methodologies at new Brain and Imaging Research Centre (BRIC) at the University of Plymouth.

The successful candidate will be part of the Eye and Vision Research Group and The Motor Control Laboratory at the Brain and Imaging Research Centre (BRIC) at the University of Plymouth.

The PhD scholar will be supervised by an interdisciplinary team of experts in vision (Dr Gunnar Schmidtmann), clinical neurology (Dr Ellie Edlmann) and neurorehabilitation (Professor Jonathan Marsden).

Please email gunnar.schmidtmann@plymouth.ac.uk if you are interested.

Apply here

Eligibility

Applicants should have a first or upper second class honours degree in an appropriate subject and preferably a relevant masters qualification.

The studentship is supported for 3 years and includes full Home tuition fees plus a stipend of £16,062 per annum (2022/23 rate). The studentship will only fully fund those applicants who are eligible for Home fees with relevant qualifications. Applicants normally required to cover International fees will have to cover the difference between the Home and the International tuition fee rates (approximately £12,670 per annum).

If you wish to discuss this project further informally, please contact Dr Gunnar Schmidtmann.

Please see a list of supporting documents to upload with your application.

This vacancy will involve working with children and/or vulnerable adults and any appointment will be subject a Disclosure and Barring Service check.

For more information on the admissions process generally, please contact doctoralcollege@plymouth.ac.uk.

New paper in Stroke and Vascular Neurology

Clinician’s perspectives in using head impulse-nystagmus-test of skew (HINTS) for acute vestibular syndrome: UK experience

Charlotte L Warner, Lisa Bunn, Nehzat Koohi, Gunnar Schmidtmann, Jennifer Freeman, Diego Kaski

Abstract

Background Acute vestibular syndrome (AVS) features continuous dizziness and may result from a benign inner ear disorder or stroke. The head impulse-nystagmus-test of skew (HINTS) bedside assessment is more sensitive than brain MRI in identifying stroke as the cause of AVS within the first 24 hours. Clinicians’ perspectives of the test in UK secondary care remains unknown. Here, we explore front-line clinicians’ perspectives of use of the HINTS for the diagnosis of AVS.

Methods Clinicians from two large UK hospitals who assess AVS patients completed a short online survey, newly designed with closed and open questions.

Results Almost half of 73 total responders reported limited (n=33), or no experience (n=19), reflected in low rates of use of HINTS (n=31). While recognising the potential utility of HINTS, many reported concerns about subjectivity, need for specialist skills and poor patient compliance. No clinicians reported high levels of confidence in performing HINTS, with 98% identifying training needs. A lack of formalised training was associated with onward specialist referrals and neuroimaging (p=0.044).

Conclusions Although the low sample size in this study limits the generalisability of findings to wider sites, our preliminary data identified barriers to the application of the HINTS in AVS patients and training needs to improve rapid, cost-effective and accurate clinical diagnosis of stroke presenting with vertigo.

Warner, C. L., Bunn, L., Koohi, N., Schmidtmann, G., Freeman, J., & Kaski, D. (2021). Clinician’s perspectives in using head impulse-nystagmus-test of skew (HINTS) for acute vestibular syndrome: UK experience. Stroke and Vascular Neurology, svn. https://doi.org/10.1136/svn-2021-001229 [PubMed] [PDF]

Hatem's poster at ECVP 2021

The role of bias in a letter acuity identification task: a noisy template model

Hatem Barhoom 1, Gunnar Schmidtmann 1, Mahesh R. Joshi 1, Paul H. Artes 1, Mark A. Georgeson 2 
1 University of Plymouth, Plymouth, UK 
2 Aston University, Birmingham, UK 

In clinical testing of visual acuity and contrast sensitivity, it is often assumed that data reflect sensory performance and observers do not exhibit strong biases for or against specific letters, but this assumption has not been extensively tested. We measured letter identification performance against letter size, spanning the resolution threshold, for 10 Sloan letters at central and paracentral visual field locations, for 10 naïve observers, using the method of single stimuli. Results showed that observers had individually different letter biases consistent across the whole range of sizes. Preferred letters were called more often and others less often than expected (group averages from 4% to 20% across letters, where the unbiased rate was 10%). A “noisy template” model was used to distinguish biases from differences in visibility. A model with varying bias across letter templates fits much better than one with sensitivity variation, but the best model combined both - having substantial biases and small variations in sensitivity across letters. The over- and under-calling decreased at larger letter sizes, but was well-predicted by templates having fixed additive response bias: with stronger inputs (larger letters) there is less opportunity for bias to influence which template gives the biggest response. The neural basis for such bias is not yet known, but a plausible candidate is the letter-recognition machinery of the temporal lobe. In the future, it will be important to investigate whether the observed response biases are likely to have a meaningful effect on clinical measures of visual performance.

Click here for higher resolution

New paper in Vision Research

Barhoom, H., Joshi, M. R., & Schmidtmann, G. (2021). The effect of response biases on resolution thresholds of Sloan letters in central and paracentral vision. Vision Research, 187, 110–119. https://doi.org/10.1016/j.visres.2021.06.002 [PDF]

Sloan letters are one of the most commonly used optotypes in clinical practice. Sloan letters have different relative legibility which could be due to three factors: perceivability, response bias, and similarity. Similarities between Sloan letters are known to be the major source of errors in threshold determination. However, little is known about the effect of response biases on the resolution thresholds. The aim of the present study was to investigate the effect of response bias and similarity on resolution thresholds of Sloan letters in central and paracentral vision. Eight subjects with normal ocular health participated in this study. Using the method of constant stimuli, we measured resolution thresholds for the Sloan letters set at 0° (central) and ± 3° eccentricity along the vertical meridian of the visual field. We calculated thresholds from data pooled across the 10 Sloan letters (pooled threshold). For further analysis we also calculated thresholds for each of the 10 Sloan letters (individual threshold). Response biases and letter similarities were determined using Luce's choice model. Results showed statistically significant differences between the mean individual thresholds of Sloan letters at the central and the upper visual field, but not at the lower visual field. For equally-sized letters at pooled threshold, unlike letter similarity, response biases showed statistically significant correlations to the differences in individual thresholds at the central, upper and lower visual field locations. For equally legible letters at individual thresholds, response biases and similarities showed no significant correlations to the differences in individual thresholds at the central, the upper and the lower visual field locations. These results suggest that, for equally-sized letters at pooled threshold, the response biases may lead to an underestimation of the pooled threshold, i.e. an overestimation of visual acuity measurements when using Sloan letters.