Nonlinear Dynamics, Psychology, and Life Sciences, Vol. 9, Iss. 3, July, 2005, pp. 281-296
@2005 Society for Chaos Theory in Psychology & Life Sciences


The Psychophysics of Tactile Amplitude Summation: A test of the Γ Nonlinear Model

Doug Mahar, Queensland University of Technology

Abstract: This research applied Gregson”s n Γ nonlinear model (Gregson 1988, 1992, 1995, 1998) to the process of tactile amplitude summation. Participants were presented with simultaneous pairs of vibrations and rated the total perceived intensity of the resultant percept as both the amplitude of the stimuli and their spatial separations were manipulated. The multidimensional response surface for each participant was then compared with that predicted by the 2 Γ Case 2 model. While the fit between data and theory was strong in all cases (mean r^2 = .86), analysis of residuals revealed evidence of a second nonlinear process. In contrast, a multivariate version of the psychophysical function was found to account for a substantially smaller proportion of the variability in the data (mean r^2 = .67). The results confirmed that summative effects similar to those observed in other modalities occur in the tactile modality, and provide an initial demonstration that the mathematics of nonlinear dynamics may help to explain the processing of tactile patterns.

Keywords: tactile perception, hypoadditivity, hyperadditivity, psychophysics, nonlinear dynamics