Vision Science 2B Research Assignment Measuring the contrast sensitivity profile Introduction The primary stimulus of the visual system is contrast. The ability to detect luminance variations across...

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Vision Science 2B Research Assignment Measuring the contrast sensitivity profile Introduction The primary stimulus of the visual system is contrast. The ability to detect luminance variations across the visual field allows for the identification of edge structure which is important in determining spatial layout and object recognition. Human perception to contrast is particularly accurate, but it is dependent on spatial frequency. The psychometric function which describes contrast detection as a function of spatial frequency is described by an inverted ‘U’ shaped function with sensitivity maximum for spatial frequencies between 2 – 8 cycles per degrees. This contrast sensitivity function (CSF) is a robust feature of visual processing and describes sensitivity to detail over a broad range of spatial scales. Because of this measuring the CSF provides a detailed way of characterizing abnormal vision. Typically, the CSF is measured using a sinusoidal grating of a particular spatial frequency and a psychophysical procedure is used to change the amplitude of the grating to reduce its apparent contrast until the grating is just visible. This point is used as a measure of the absolute contrast threshold (see Contrast Sensitivity lecture for details). Dividing 1 by the contrast threshold (1/Threshold) provides an estimate of contrast sensitivity. This procedure is then repeated for a range of spatial frequencies from low to high. A student wishes to see whether and how the CSF is affected by glaucoma and repeats the abovementioned experiment with stimuli of 1, 2, 4, 8 and 16 cpd presented for 20 participants -10 normal vision and 10 with glaucoma. Each participant is tested at all cpd. The results of this experiment can be accessed via an excel file (uploaded into Moodle Week 8). The data set that you will use will be the one corresponding to the last digit of your z id. Input your data in the tables below and perform the following analyses: Normal group Spatial Frequency Participant 1 2 4 8 16 1 121 202 247 147 86 2 129 191 262 138 85 3 135 197 244 137 74 4 137 202 239 148 93 5 129 188 248 145 76 6 135 207 236 137 79 7 123 213 265 140 95 8 123 188 253 136 77 9 132 205 264 154 82 10 134 199 247 150 89 Mean And SD glaucoma group Spatial Frequency Participant 1 2 4 8 16 1 91 149 195 101 15 2 95 159 199 89 7 3 101 155 195 77 34 4 92 161 195 79 14 5 83 148 207 91 28 6 109 169 108 100 21 7 87 150 197 89 19 8 101 173 196 85 20 9 110 146 211 78 13 10 109 171 204 99 29 Mean and SD Descriptive Statistics 1) For each spatial frequency, compute the mean and standard deviation for all participants for normal and glaucoma groups. What do these two statistical measures represent? 2 marks 2) Use graphpad prism, plot on the same figure, the mean and standard deviation for both normal and glaucoma groups as different symbols. Describe in words how: 1) contrast sensitivity changes with spatial frequency, 2) why does the CSF have an inverted U shape and 3) whether and how the CSF curve differs between normal and glaucoma groups. 4 marks 3) What might account for the difference/lack of difference in CSF between normal and glaucoma? 10 marks Inferential statistics 4) Separately for each group (i.e., normal and glaucoma), perform a correlation analysis between the mean contrast sensitivity and spatial frequency. What type of correlation should you use and why? 4 marks Report the strength and direction of the correlations, and in your own words describe the relationship and whether this relationship is the same for normal and glaucoma participants. 4 marks 5) Perform two separate t-tests to determine whether contrast sensitivity is different between normal and glaucoma for spatial frequencies of 1 and 8 cpd (N.B. don’t compare between 1 and 8 cpd but compare between normal and glaucoma separately for data measured at 1 and 8 cpd). For each spatial frequency tested, report the t-statistic, df and p value and make a statement regarding what the t test shows regarding whether there is a difference between normal and glaucoma groups for each of the two spatial frequency tested. 10 marks 6) Separately for normal and glaucoma, perform a 1-way ANOVA to determine whether contrast sensitivity significantly changes with spatial frequency. For both analyses (normal and glaucoma) report the F statistic, df and p value and make a statement regarding the outcomes of the test. 8 marks What are the advantages of performing an ANOVA as compared to conducting multiple t-tests to compare means? 2 marks What type of ANOVA should be performed and why? 2 marks General questions 7) Suggest two ways in which the experiment could be conducted to reduce variability. 4 marks 8) Describe and discuss two visual disorders that are known to affect contrast sensitivity. 8 marks Due Friday, week 10 (Moodle Turnitin submission). Vision Science 2B Research Assignment Introduction Normal group
Nov 22, 2021
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