Chaotic dynamics in ear plethysmogram system was studied in both tracking experiment and a mathematical model. The experiments were conducted by using of a driving handle to track moving targets on a PC screen. The moving targets were driven by signals of different predictabilities with sin wave, chaotic and random waves. We found that chaos happened in ear plethysmogram and there were changes in the chaotic dynamics during tracking the signals with different predictable natures. The largest Lyapunov exponent of the plethysmograms was found to be significant higher during tracking chaotic signals. To understand how the chaos arises and to explain the changes in the Lyapunov exponent in ear plethysmograms in experiments, a mathematical model consisting of baroreflex feedback and autonomous interactions was proposed and studied numerically. The increase of the largest Lyapunov exponent in plethysmograms was explained successfully in the model in relation to the increased chaoticity, and hence the increased active temporal information processing in higher cerebral region.