These results do not support the theory of the existence of a magnocellular deficit in dyslexic individuals. Our ability to see the fine details of objects diminishes when the target of interest moves at a high speed. The stimulus for Vernier discrimination was a pair of vertical abutting lines and that for letter resolution was a four-orientation letter 'T'. Bandwidth of filters was 1.5 octaves. Our results show that both Vernier and letter acuities increase by a factor of two for each one-octave decrease in filter spatial frequency.
Acuities are also inversely proportional to stimulus contrast.
For stimuli of higher spatial-frequencies, thresholds remain essentially constant until the velocity corresponds to a temporal frequency of about 25 Hz, and increase thereafter. Our results indicate that spatial thresholds for moving stimuli are limited by the spatial and temporal frequencies of the mechanism that mediates the spatial task, and the stimulus contrast that is available within the mechanism. David A. Goss, OD, PhD Professor IU School of Optometry Myopia has generally been viewed as an anomaly or as a failure of emmetropization. A theory in which retinal image clarity mediates the rate of posterior segment growth will be discussed, along with suggestions for research and clinical practice. Time permitting, a discussion of Dr. Braun's research into tuberculosis in prehistoric Native Americans will follow.