John Siderov


  • University of Huddersfield Queensgate Huddersfield HD1 3DH

    United Kingdom

Accepting PhD Students

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Personal profile


A particular focus of my research is to investigate and understand the problem of visual crowding, where the recognition of letter targets (as indeed other objects in visual space) is disrupted by the presence of nearby contours. Our work has attracted international interest. We have demonstrated that in central vision (i.e. foveal) for near threshold stimuli, crowding operates over a fixed spatial distance irrespective of target size, which contradicts a popular explanation of crowding (Siderov J., Waugh S.J. & Bedell H.E. Foveal contour interaction for low contrast acuity targets. Vision Research, 2013; 77: 10-13 and Siderov J., Waugh S.J. & Bedell H.E. Foveal contour interaction on the edge: Response to Drs Coates and Levi. Vision Research 2014; 96:145-148). We were the first to show that the intensity of foveal crowding reduces under low levels of luminance (mesopic) (Bedell H.E., Siderov J., Waugh S.J., Zemanova R., Pluhacek F., & Musilova L. Contour interaction for foveal acuity targets at different luminance. Vision Research, 2013; 89:90-95) but not under total darkness (scotopic luminance) (Musilova L., Pluhacek F., Marten-Ellis S.M., Bedell H.E., & Siderov J. Contour interaction under photopic and scotopic conditions. Journal of Vision, 2018; 18(5): 1-11). This finding has implications when assessing vision clinically under low luminances (Pluhacek F. & Siderov J. Mesopic visual acuity is less crowded. Graefe’s Archive for Clinical and Experimental Ophthalmology, 2018. /


We have confirmed experimentally early suggestions that letter recognition in children and in patients with amblyopia is crowded through a combination of low level spatial interactions (contour interaction) in addition to higher level influences through putative attentive mechanisms or possibly factors relating to eye movements (Bedell H.E., Siderov J., Formankiewicz, M.A., Waugh S.J., & Aydin S. Evidence for an eye- movement contribution to normal foveal crowding. Optometry and Vision Science 2015; 92: 237-245). An additional finding suggests a different time course for the development of visual acuity in children based on how crowding develops, which has not previously been reported (Norgett Y. & Siderov J. Effect of test chart configuration on crowding in strabismic amblyopia. Journal of Vision. 2017; 17: 1-14; Norgett Y. & Siderov J. Foveal crowding differs in children and adults. Journal of Vision, 2014; 14: 1-10 and Norgett Y. & Siderov J. Crowding in children’s visual acuity tests – effect of test design and age. Optometry and Vision Science, 2011; 88(8): 920-927).

External positions

Member, Education Visitor Panel, General Optical Council

Feb 2019 → …

Assessor non_UK registrations, General Optical Council

2017 → …


  • vision, crowding, stereopsis, amblyopia

Fingerprint Dive into the research topics where John Siderov is active. These topic labels come from the works of this person. Together they form a unique fingerprint.

Crowding Medicine & Life Sciences
Visual Acuity Medicine & Life Sciences
Eye Movements Medicine & Life Sciences
Amblyopia Medicine & Life Sciences
Czech Republic Medicine & Life Sciences
Visual Fields Medicine & Life Sciences
Saccades Medicine & Life Sciences
Tremor Medicine & Life Sciences

Network Recent external collaboration on country level. Dive into details by clicking on the dots.

Research Output 2014 2019

Lateral interference, effects of flankers and reference bar configuration on foveal depth discrimination thresholds

Ocansey, S., Osuobeni, E. & Siderov, J., 1 Mar 2019, In : Vision Research. 156, p. 96-104 9 p.

Research output: Contribution to journalArticle

1 Citation (Scopus)

Assessment of Visual Acuity in Children Using Crowded Lea Symbol Charts

Sailoganathan, A., Rou, L. X., Buja, K. A. & Siderov, J., 1 Aug 2018, In : Optometry and Vision Science. 95, 8, p. 643-647 5 p.

Research output: Contribution to journalArticle

Visual Acuity
1 Citation (Scopus)

A standardized logarithm of the minimum angle of resolution visual acuity chart in Hindi

Sailoganathan, A., Osuobeni, E. P. & Siderov, J., 1 May 2018, In : Indian Journal of Ophthalmology. 66, 5, p. 634-640 7 p.

Research output: Contribution to journalArticle

Open Access
Visual Acuity
Confidence Intervals

Contour interaction under photopic and scotopic conditions

Musilová, L., Pluháček, F., Marten-Ellis, S. M., Bedell, H. E. & Siderov, J., 15 Jun 2018, In : Journal of Vision. 18, 6, 11 p., 5.

Research output: Contribution to journalArticle

Open Access
Czech Republic
Visual Fields

Mesopic visual acuity is less crowded

Pluháček, F. & Siderov, J., 1 Sep 2018, In : Graefe's Archive for Clinical and Experimental Ophthalmology. 256, 9, p. 1739-1746 8 p.

Research output: Contribution to journalArticle

Visual Acuity