Title

Tracking the elusive effect of the Muller-Lyer figure

Date of Completion

January 2003

Keywords

Biology, Neuroscience|Psychology, Experimental|Physics, Optics

Degree

Ph.D.

Abstract

The perceptual scaling of extent for an arrows-only Müller-Lyer figure is examined from the theoretical framework of Intentional Dynamics. This framework defines effects that goal constraints have on a perceiving-acting cycle within an event perception explanation of this century-old problem. ^ The classic strain effect and a novel rotational effect are proposed as arising from an ecology of a pair of dual constraints: the light and figure plus the perceptual system and muscle-control system. This ecology is assumed to function successfully under the soft constraint of an intention. This approach unifies and extends past research through modeling with finite element methods the light field for which the figure serves as boundary conditions. ^ Participant data significantly matched the strain and rotational effects as predicted by the light field model. The experimental apparatus permitted participants to see a black figure on a computer screen's white background and to track and report perceptions with mouse movements. Experiments included static (presented in ordered and random sequences) and dynamically moving figure layouts. In the first sub-set of Experiment Set I, participants controlled the length of a report bar to “fit the gap” between the figure's vertices. For the second sub-set, independent and dependent variables were swapped; participants controlled the figure's angle magnitude so that the gap between vertices matched the length of a presented report bar. The intention remained to “fit the gap.” ^ In Experiment Set II, participants adjusted a Müller-Lyer figure about its midpoint to report whether a rotational effect occurred. The figure contained asymmetrical phase relations among its fins. The experimental intention was to “keep the figure horizontal.” ^ Experiments elicited expected Müller-Lyer effects (strain or rotation) with no significant difference among presentation methods such that the light field's event trace generatively specified the effect. Participants tracked either effect when the figure moved dynamically. The light field model significantly predicted participant judgments of inter-vertex extent and figure orientation. These tests provide evidence that reported Müller-Lyer effects exist in the light field's structure. ^