Alan J Courtney | PubMed Health

PubMed2005

Quantifying visual field shape for improving accuracy of search performance prediction.

The current study calculated a set of 16 shape indices of six subjects (4 men and 2 women, 21-28 years old) for easy and precise quantification of visual lobe shapes using Visual Lobe Measurement System (VILOMS) software. The indices can be used in mathematical models of visual search for better understanding of search behaviour and higher accuracy of search performance prediction. General patterns in the shape indices showed that visual lobes of the subjects were slightly irregular, with low sphericity, a moderately rough boundary, horizontally elongated and slightly asymmetric along both axes. Given the complex relationships among visual lobe area, lobe shape, and search strategy, it seems that a more detailed analysis than hitherto attempted will be necessary. Quantifying lobe shape with the 16 shape indexes is a useful step to performing such analysis.

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PubMed2002

Visual performance on detection tasks with double-targets of the same and different difficulty.

This paper reports a study of measurement of horizontal visual sensitivity limits for 16 subjects in single-target and double-targets detection tasks. Two phases of tests were conducted in the double-targets task; targets of the same difficulty were tested in phase one while targets of different difficulty were tested in phase two. The range of sensitivity for the double-targets test was found to be smaller than that for single-target in both the same and different target difficulty cases. The presence of another target was found to affect performance to a marked degree. Interference effect of the difficult target on detection of the easy one was greater than that of the easy one on the detection of the difficult one. Performance decrement was noted when correct percentage detection was plotted against eccentricity of target in both the single-target and double-targets tests. Nevertheless, the non-significant correlation found between the performance for the two tasks demonstrated that it was impossible to predict quantitatively ability for detection of double targets from the data for single targets. This indicated probable problems in generalizing data for single target visual lobes to those for multiple targets. Also lobe area values obtained from measurements using a single-target task cannot be applied in a mathematical model for situations with multiple occurrences of targets.

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