Using a probabilistic model, exact and approximate probability density func
tions (PDFs) for city-block distances and distance ratios are developed. Ti
le model assumes that stimuli can be represented by random vectors having m
ultivariate normal distributions. Comparisons with the more common Euclidea
n PDFs are presented. The potential ability of the proposed model to correc
tly detect Euclidean and city-block metrics is briefly investigated. These
results are then contrasted to those obtained using a deterministic, nonmet
ric model. (C) 2001 Academic Press.