Perception is sensation with added complexity due to factors such as memories and emotions. Yoga practice influences perception in three ways: (1) by increasing perceptual sensitivity, (2) by selectively `shutting out’ undesirable stimuli, and (3) by changing distorted perception, which occurs in schizophrenia. Practicing yoga improved auditory and visual perception, by increasing sensitivity to various characteristics of the stimuli (e.g., intensity, frequency). Also, electrophysiological studies using evoked potentials have shown that during yoga practice the transmission of sensory information is facilitated. These studies suggest several applications of yoga practice, in activities ranging from aviation to art. Interestingly, other studies suggest that yoga practice can also help to `shut off’ undesirable external stimuli, which is possibly due to cortical feedback connections to the sensory pathway. It is also possible that through changes in cognitive factors yoga influences perception, so that even though the stimulus is `sensed’ it is not disturbing. This concept has been studied using yoga to help persons with chronic pain to willfully ignore it. Finally, preliminary studies have shown that yoga practice may modify distorted perception in conditions such as schizophrenia. Hence, there is sufficient research to support the idea that yoga practice influences perception in different ways, with varied applications.

Perception is the process of interpretation, organization, and elaborating the `raw materials’ of sensation (1). Sensation involves sensory receptors and pathways, whereas perception is a cognitive process. The actual perception of a sensation depends on factors such as what has been learned, memories, and emotions. It is also important to remember that while perception usually refers to sensory stimuli, this definition can be extended to include the perception of situations.
Recordings of middle latency auditory evoked potentials (AEP-MLRs) have shown that the practice of ujjayi pranayama modifies the AEP-MLRs components in two ways. A specific component (the Na wave) has reduced latency and increased amplitude during pranayama practice (2). These results suggest that this practice facilitates the processing of auditory information at mesencephalic and diencephalic levels. A similar result was also seen during the practice of meditation on the syllable Om (3), where subjects who had more than ten years of meditation experience, showed an increase in the Na wave amplitude and a decrease in its’ latency while mentally repeating (Om). No such effect was seen when the same subjects mentally repeated `one’, during a control session, for comparison.
These electrophysiological data are corroborated by neuropsychological studies. Previous studies on meditation have shown significant changes in perception, attention and cognition (4). Brown and Engler in 1980 (5), reported that meditators were found to be more sensitive to subtle aspects of color and shading of the Rorschach test inkblots, than they had been before meditation. Two studies on the Critical Flicker Fusion Frequency have shown that perceptual sensitivity is not restricted to subtle aspects of the stimulus alone, as detection of a high frequency flickering stimulus was found to improve following yoga training (6,7). A study on the degree of a visual geometric illusion, based on Müller-Lyer lines showed that a combination of focusing and defocusing yoga visual exercises reduces optical illusion more than focusing alone (8). These studies were conducted on adult subjects with varying durations of yoga training. It was reported in a recent study on Critical Flicker Fusion Frequency and optical illusion on children who practiced yoga for a shorter duration of 10 days that there was also a significant improvement following the practice of yoga (9). To perceive an optical illusion with minimal error and for accurate depth perception the spatial component of visual perception is necessary (10). The decrease in the degree of optical illusi