Premium
The effect of mental effort on open‐ and closed‐loop accommodation
Author(s) -
Winn B.,
Gilmartin B.,
Mortimer L. C.,
Edwards N. R.
Publication year - 1991
Publication title -
ophthalmic and physiological optics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.147
H-Index - 66
eISSN - 1475-1313
pISSN - 0275-5408
DOI - 10.1111/j.1475-1313.1991.tb00234.x
Subject(s) - accommodation , monocular , emmetropia , stimulus (psychology) , psychology , audiology , optometry , refractive error , cognitive psychology , optics , physics , medicine , visual acuity , neuroscience
The accommodative response to stimuli in normal visual environments is determined by a complex and subtle integration of optical and non‐optical factors. Mental effort associated with the visual task can modify significantly the steady‐state accommodative level, but. owing to the diversity of experimental designs, there is no clear consensus on the mechanisms involved. Changes in the accommodation response of ten emmetropic subjects (mean (±SD) age = 20.4 ± 4.5 years) under open‐ and closed‐loop conditions were investigated for three levels of mental activity. (1) A passive task whereby subjects simply read letters, to themselves. (2) A stimulus‐ dependent task (SDT) whereby subjects are instructed to respond only when the letter ‘e’ appears in one of a series of presentations. (3) A stimulus‐independent task (SIT) whereby subjects count backwards in sevens to themselves while viewing the target. An objective infra‐red (IR) optometer was used in its static mode of operation to make monocular measurements of accommodation under monocular viewing conditions. Open‐loop conditions were achieved by placing a pinhole (0.5mm diameter), drilled into an IR filter. 12mm in front of the eye. Under closed‐loop conditions the mean accommodation response for passive viewing of the near target was +3.08D. A significant ( F = 5.45 d.f. 9,18 P < 0.005) accommodative shift induced by mental effort in the mean response of +0.17 D occurred for the SDT, The SIT induced a mean shift of −0.05 D which was not significantly different to the passive viewing response. A significant negative correlation between the magnitude of the passive open‐loop response and the size of the shift induced by mental effort was found for both tasks (SIT: y = 1.314 − 0.815 x R = 0.86. SDT: y = 2.169 − 0.821 x R = 0.70). With respect to zero shift, the relationship was pivotal about 1.61 for SIT and 2.64 D for SDT. It is proposed that when the effect of optical feedback is minimized a significant interaction occurs between mental effort and perceived proximity.