The Effects of Pitch on Perception between Visual and Auditory Stimulus

Jessica Bloomfield and Heidi Bensinger: 09jabloo@alma.edu 09hlbens@alma.edu, Alma College

INTRODUCION

Efron (1970) did studies that compared an auditory and a visual stimulus. Participants were asked whether or not the offset of a given stimulus gave way to the onset of the second stimulus. He found that there was a fixed minimum duration for a given stimulus. Rowland and Emmerich (1978) did a study on the reaction time of a person to a given stimulus. They found that the longer the stimulus the better the participant did on precieving the end of the stimulus. A study done by David Alais and Simon Carlile (2004) found that there was a delay aligning the visual stimulus with the auditory stimulus when the auditory stimulus sounded further away. In this study we are hoping to find whether or not pitch will affect the precieved duration of an audio stimulus.

METHODS

Subjects-
For this experiment, fifteen college students volunteered.

Appartus and Stimuli-
The test was performed on a PC laptop, using a QuickTime file to present the audio and visual stimuli. The audio stimuli were presented in the form of a tone that is the same as low, middle and high C on a musical scale. The visual stimuli were a flash shown as a white frame presented for a brief period of time. The tones were one and a half seconds long with intervals of two and a half seconds between each tone. The flash had a duration of two frames, which is about a fifteenth of a second. The flash occurred at the end of the tone, or .15 seconds before or after the end of the tone.

Procedure-
Subjects were told that they had to mark down, using a check or X-mark, when they saw a flash of light in comparison to a tone being played. The subjects were given a sheet of paper numbered one to ten with three separate columns marked Before, During and After on which to mark where they believed the flash to be. The subjects were then seated at a PC laptop where they were asked to put on a pair of noise canceling headphones. This would be to reduce any sort of outside interference. The researcher then pulled up the QuickTime movie player program. The subjects were required to watch the screen. Notes were being played while the screen was black and would flash white at random points during the notes being played. The subjects would then record where they saw the flash relative to the ending of the tone.


RESULTS


Subjects were most accurate at determining the flash location if it occurred at or after the end of the tone. This was consistent with all tones, though the accuracy increased with lower pitches. When determining if the flash occurred before the end of the tone, the accuracy rate was 15.3%. In comparison, when determining if the flash occurred after the end of the tone, the accuracy rate was 59.6%. For the remaining tone, when the flash occurred at the end of the tone, the accuracy was also 59.5%.


Figure One

DISCUSSION


The data that were gathered from this experiment went to show that pitch does affect the ability to perceive when a flash occurs. The participants were able to more correctly perceive when the flash occurred during a lower pitch rather than the higher one. The lower pitch might be able to be perceived more accurately because the sound waves are larger. With this larger wavelength it is easier to hear the exact ending of the tone, rather than the shorter one that is higher in pitch. Participants were not nearly as accurate with the higher pitches as they were with the lower pitches.

There were several participants who answered straight down one column or another about where they saw the flashes. Perhaps these participants did not take the study as seriously as the rest of the participants did. Another possibility is that these participants were not susceptible to the different pitches like the rest of their peers were. Another phenomenon that was observed was that overall the participants had a hard time judging whether or not the flash occurred before the end of the tone. When a tone was presented with a flash that ended before the tone was finished, most perceived the flash to be at the end of tone rather than before it. If the flash was not perceived at the end of the tone than it was perceived after the tone. This was consistent with all of the pitches. Efron (1970) had found that there was a set time in between two stimuli that a person could perceive a difference. Perhaps the flash occurring before the end of the tone was this phenomenon that Efron had described. Another possibility the flash occurred too quickly while the other stimulus was being presented so that there was no observable difference.

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