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Kingdom FAA, Read JCA, Hibbard PB, May KA. Special issue: Coding strategies in binocular vision and stereopsis. Vision Res 2021; 193:107989. [PMID: 34973631 DOI: 10.1016/j.visres.2021.107989] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Reena Durai CV, Rajendran S, Webster MA, Vempati S, Bharadwaj SR. The magnitude of monocular light attenuation required to elicit the Pulfrich illusion. Vision Res 2021; 187:85-93. [PMID: 34225133 PMCID: PMC8363548 DOI: 10.1016/j.visres.2021.06.008] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2020] [Revised: 06/17/2021] [Accepted: 06/19/2021] [Indexed: 11/17/2022]
Abstract
In the Pulfrich illusion, the depth of a moving object is misperceived due to induced retinal disparity and/or interocular velocity differences arising from differences in luminance, contrast, or spatial frequency between the two eyes. These effects have been shown to occur both for visual deficits and for optical corrections that introduce significant binocular differences between the retinal images. However, it remains unknown to what extent the illusion might arise given normal variation between the eyes, such as natural interocular variation in pupil diameter (anisocoria). To assess this, we examined the threshold interocular retinal illuminance difference required to experience illusory depth in two random-dot fields moving in opposite directions in 24 normally-sighted observers with dilated pupils. Interocular difference in retinal illuminance was induced by placing neutral density filters of different intensities before the left eye. A minority of subjects (n = 8) did not provide meaningful data on changes in the experience of illusory depth with interocular difference in retinal illuminance and four subjects showed biases >±10% from the 50% point of subjective equality in the psychometric function. For the remaining 12 participants, the retinal illuminance had to differ by approximately 40% for the depth between the planes to become visible at threshold levels. This difference was approximately constant over a range of absolute luminance levels from 10 to 80 cd/m2. Our results suggest that while motion-in-depth illusions due to interocular differences in retinal illuminance may be pronounced in certain ophthalmic diseases or following certain optical interventions, it is unlikely to be manifest as a result of normal interocular variations in retinal illuminance. Further, our results also point towards the existence of substantial individual differences in the experience of what is otherwise thought of as a readily appreciable motion-in-depth illusion.
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Affiliation(s)
- C Vijay Reena Durai
- Brien Holden Institute of Optometry and Vision Sciences, LV Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India; Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, LV Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India
| | | | | | - Sandeep Vempati
- Center for Innovation, LV Prasad Eye Institute, Hyderabad 500034, Telangana, India
| | - Shrikant R Bharadwaj
- Brien Holden Institute of Optometry and Vision Sciences, LV Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India; Prof. Brien Holden Eye Research Centre, Hyderabad Eye Research Foundation, LV Prasad Eye Institute, Road no. 2, Banjara Hills, Hyderabad 500034, Telangana, India.
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