DENSITY FLUCTUATION IN BROWNIAN-MOTION AND ITS SIGNIFICANCE IN OLFACTION

Sensory perception might be defined, in part, as that activity whereby changes in the environment are detected. Rom this point of view, fluc tuations in a stimulus are more important than the mean stimulus inten sity. In this paper, we are concerned primarily with the chemical sens es in which the stimulus consists of molecules undergoing random motio n in a fluid. We extend Smoluchowski's model of Brownian motion to inc lude an analysis of the variance of observed density fluctuations (var iance because we are concerned with changes rather than mean values). A computer simulation of Brownian motion in two dimensions was develop ed and run on the Cray supercomputer. It is shown that density fluctua tions in the computer-simulated data fall within the constraints calcu lated from the analysis of variance, but that published experimental d ata deviate somewhat from the theoretical constraints. We then apply t he computer simulations to show that successive density measurements b y olfactory cells are probably highly correlated, which can produce an olfactory ''illusion'' during the early moments of the process of sme lling.