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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)
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.
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.
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.
<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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