The DSM (DSM-5) defines autism as a complex disorder that affects the brains normal development of social and communication skills.
In the 1950s Individuals with characteristics of autistic traits, such as touching and smelling instead of listening were assumed to have perceptual abnormalities (Goldfarb, Braunstein & Lorge, 1956). However, other research indicates that autistic children show no difference in perceptual processing than those without autism. There is also evidence that demonstrates autistic individuals perform better at some tasks, for example being less likely to succumb to two-dimensional images than other groups (Happé 1996).
The findings from these studies led to the development of the weak central coherence theory. This theory proposes the view that autistic people focus on the finer details of tasks (local level), whereas healthy individuals focus on the overall picture (global level). This is what allows autistic individuals to ignore distracting information in embedded tasks (Shah and Firth 1993). Plaisted et al (1999) argued the local aspects of a stimulus are processed by high spatial frequency channels and the global characteristics of a stimulus are processed by the low spatial frequency channels. He suggested the difference in processing between autistic and healthy individuals is due to abnormally high or low activity in visual channels in the brain. However, a study by Milne et al (2002) found that abnormally low activity in spatial frequency channels is the cause of difference seen in autistic people. The activity in the visual channels can be measured using a motion coherence task.
A motion coherence task involves participants judging the overall direction of moving dots amongst a small number that move randomly. Some dots are moving in one direction (coherent direction) whereas the other dots change direction constantly. Motion coherence threshold is the lowest proportion of dots participants can distinguish as moving in a coherent direction. Spencer et al (2000) like Milne’s study found motion perception in autistic children was worse (has a higher motion coherence threshold) than control groups. However, in Milne’s study some individuals in the autistic group performed better than healthy children indicating following studies should compare motion performance in normally-developing people.
As previous research has suggested individuals with higher autism scores will score worse on the motion coherence task. Measuring coherence performance will involve us recording each participants accuracy and reaction time on each trail, two hypotheses will be tested. The first hypothesis states: accuracy will be significantly lower for individuals in the higher autism score group. The second hypothesis that will be tested is: reaction times will be significantly longer for individuals in the higher autism score group. Participants will be classed into low and high autistic trait groups to measure the hypotheses.