Introduction: The influence of stress or physical tiredness onto the perception of visual illusions is rarely studied leading to contradictory results. The mechanism of influence of such factors can be based on the changes in attentional processes. The physical arousal influences the attentional processes by narrowing of attention to the central components of the task, and the changes in attentional pattern, in turn, may change the illusion’s strength. The aim of the present study was to check the dependence of the illusion’s strength on the short-term physical exercise, Harvard step test, using as verbal as sensorimotor responses.
Methods: The control and experimental groups have a three-stage testing twice, before and after 5-min rest or Harvard step test respectively. These testing consists of measurement of the heart rate with the help of pulsometer, “verbal response” and “sensorimotor response” stages. At “verbal response” stage the participants had to tell on how many percent differs the length of the central shafts of the stimuli. At “sensorimotor response” stage the participant moved his right hand across the touch screen monitor; then the stimulus disappeared and the participant repeated such movements over the empty touch screen. The relative strengths of the illusions and the mean movements speed were calculated. The same 15 stimuli were used at “verbal response” and at “sensorimotor response” stages. At first, we present to participants five neutral stimuli consisting of two shafts without any flanks, then five stimuli eliciting Müller-Lyer illusion (upper shaft looks longer), then five stimuli eliciting classical Ponzo illusion.
Results and discussion: We failed to find the influence of fatigue elicited by short-term physical exercise onto the illusion’s strength. The similar results were obtained in (Lybrand et al., 1954) with the help of Müller-Lyer illusion though the physical load of their participants was much higher. We should underline that even the researches of sensory deprivation performed approximately in the one experimental design with the help of the one Müller-Lyer illusion lead to very different results. E.g., Freedman et al. (1961) claimed that the variability of the individual alignments was significantly greater for the control subjects while the mean strength of the illusion stayed unchanged. In contrast, Ueno and Tada (1965) obtained an increase in average magnitude of the illusion, and Suzuki et al. (1965) had received its decrease.