June 2015
Volume 56, Issue 7
Free
ARVO Annual Meeting Abstract  |   June 2015
The Effect of Room Length on Perceived Egocentric Distance in Darkness
Author Affiliations & Notes
  • Susan A Kelly
    Basic Science, Illinois College of Optometry, Chicago, IL
  • Footnotes
    Commercial Relationships Susan Kelly, None
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Investigative Ophthalmology & Visual Science June 2015, Vol.56, 2924. doi:
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      Susan A Kelly; The Effect of Room Length on Perceived Egocentric Distance in Darkness. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2924.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose: In the dark the perceived egocentric distance of a self-illuminated target has been reported to be underestimated by a number of laboratories. This underestimation is of about the same magnitude whether perceived distance is measured using a verbal magnitude estimation task or a blind-walking motor task. We have investigated the effect of the room dimensions on the perceived egocentric distance and found this variable to be significantly affected by room length.

Methods: Two groups of visually normal subjects were tested, all of whom had an eye exam within the past year. One group was tested in a room 3.8m wide and 8m long (n=20). The other group was tested in a room 11m wide and 9m long (n=15). Subjects clearly viewed the testing space prior to the testing session.<br /> <br /> After obtaining informed consent, subjects were instructed to monocularly observe the perceived distance and height of a small, self-illuminated, red target placed on the floor of an otherwise dark room. The target was randomly located at 4 distances between 1.5 and 7.5m. When ready subjects occluded their eye and blind-walked to the remembered target location. They indicated with the tip of their index finger the perceived target height.

Results: A two-way analysis of variance (mixed design) was used to compare the perceived distances for the two testing spaces (IBM SPSS). The interaction effect of Distance*Room was significant (F=7.48, p<0.000). Independent t tests with Bonferroni correction indicated that perceived target distances varied significantly between testing spaces except at 1.5m. The best-fit power function exponents for the two spaces are listed below, along with those obtained from previously published data (width x length in m):1) Philbeck and Loomis (1997) 4.3x7.3; 0.54 2) Kelly (2014) 3.8x8; 0.67 3) Kelly (2014) 11x9; 0.89 4) Philbeck and Loomis (1997) 1.8x18; 0.89.

Conclusions: <br /> 1. The perceived distance is significantly foreshortened when measured in a shorter room than in a longer testing space.<br /> 2. The perceived height of self-illuminated target is significantly higher in a shorter room than in a longer testing space.<br /> 3. The exponent for perceived distance is smaller the shorter the testing space, indicating spatial compression occurs more in short rooms.<br /> 4. There are a number of potential explanations for this effect which will be discussed.

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