Are psychophysical functions derived from line bisection reliable?

Psychophysical functions are used to characterize both normal perception and altered perception among patients with neglect, yet the reliability of these functions is rarely examined. The present study examined two-week, test-retest reliability for power functions derived from line bisection data among 58 normal, young and old, male and female subjects. Power function exponents and constants were, at best, moderately reliable over time. The size of the exponent tended to decrease at retesting. Reliability coefficients varied by age and gender; they were highly significant for young men, marginally significant for older men, and non-significant for women. Race influenced reliability as coefficients were significant for Caucasian subjects but not for African American subjects. Age and gender effects in this study parallel those in the literature on pseudoneglect, and they may reflect hemispheric differences in visuo-spatial processing, magnitude estimation, or both.