Contrast Sensitivity Function

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  • Topic: Grating, Spatial frequency, Wave
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  • Published : April 18, 2012
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SPA Lab 4: CONTRAST SENSITIVITY FUNCTION
Ciara Dubose
University of Central Oklahoma

Abstract
The purpose for this experiment is to determine at which spatial frequency does a participant’s visual acuity for a contrast sensitivity function display a peak performance across different sine – wave gratings. The ability to contrast sensitivity is useful in everyday life, more than people imagine. These contrast sensitivity functions focus primarily on the participants’ ability to detect accurately the presence of a sine – wave grating across different levels of contrast. The one way repeated participants design indicated there was a reliable effect of spatial frequency on contrast sensitivity. The conclusions of this experiment suggest rejecting the null hypothesis that spatial frequency will produce no significant effect on contrast sensitivity. SPA Lab 4: CONTRAST SENSIVITY FUNCTION

The purpose for this experiment is to distinguish the spatial frequency at which a participant’s contrast sensitivity peaks (Schieber, 2010). The issue of interest for this experiment is to determine the level of spatial frequency that contrast sensitivity is most accurate. The contrast sensitivity function is important because it allows the experimenter to measure the participant’s ability to determine the presence of differing sine – wave gratings (Coren, Ward, & Enns, 2003). This particular contrast sensitivity function measures the ability to perceive low – contrast targets over a wide range of different frequencies and dimensions (Schieber, 2010). One modern day example of an audition contrast sensitivity function is when a person is performing sound gating, or filtering out the unnecessary background noise from a recording by setting a predetermined level at which the sounds are to be interpreted as noise. This experiment used the different levels of spatial frequencies for sine – wave gratings to assist in measuring visual acuity using contrast sensitivity (Schieber, 2010). One example of a contrast sensitivity function that used to test visual acuity is the Snellen Eye Chart, which measures visual acuity, starting with bigger letters towards the top of the chart and then shrinking the font size of the following letters. When individuals highlight their ability to distinguish dark targets among lighter backgrounds among a diminishing contrast could be when a person is reading a book outside as the sun goes down. When the light emitted from the sun is not sufficient to provide the amount of illumination necessary for a person to determine letters on a page as words, then that person is actively performing a contrast sensitivity function. This example also illustrates that when the contrast is low the participant’s ability to determine the identity or presence of a target becomes impaired.

A contrast sensitivity function is one that assists in distinguishing a participant’s ability to identify the presence of a target spatial frequency among differing spatial frequencies or the absence of a spatial frequency. A contrast sensitivity function also involves the process in which the brain replicates only the spatial frequencies that a person can detect. The method that used to measure the contrast sensitivity in humans is the contrast matching procedure. In a contrast, matching procedure a participant had shown an image also consecutive image with either a higher spatial frequency or none at all. The participant must determine which of the two images shown contained the grated surface or the more heavily grated surface. The measure that this particular function produces used to distinguish the person’s contrast threshold. The degree of contrast between the light and the dark surfaces must be, to determine a reliable change, is often referred to as the contrast threshold. A contrast sensitivity matching function is one in which a participant is asked to distinguish between an early image and a late image and to...
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