Degree Name

Doctor of Philosophy


Department of Psychology


The strongest differentiation between the transient (magnocellular) and sustained (parvocellular) visual pathways, is in terms of colour processing, with the transient system generally considered to be colour insensitive. This distinction is obvious in both the anatomy and physiology of the visual system (e.g., Wiesel & Hubel 1966; Gouras 1968; De Valois, Abramov & Jacobs 1966; Schiller & Malpeli 1977). Both physiological (e.g., Wiesel & Hubel 1966; Derrington, Krauskopf & Lennie 1984) and psychophysical evidence (e.g., Williams, Breitmeyer, Lovegrove & Gutierrez 1991) has suggested that transient cells may be suppressed by diffuse red light. The possible effect of blue light is, however, more complex. No known physiological studies have demonstrated an effect of blue light on transient system activity, nevertheless, psychophysical studies have demonstrated what has been interpreted to reflect an increase in the speed and extent of transient system activity with blue light (e.g., Williams et al 1991; Williams, Weisstein & LeCluyse 1990; Williams & LeCluyse 1992). This conflict is serious, as no explanation has been extended to indicate how transient system activity is affected by blue light, and justifies further research, both from a theoretical aspect, and for the remedial implications for specific reading disabled children, many of whom are hypothesised to suffer a transient system deficit (Williams & Lovegrove 1992). Furthermore, previous psychophysical experiments appear to suffer methodological limitations such as small sample sizes. The aim therefore, was to explore the extent and range of the effects of both red and blue light on transient system activity over different psychophysical measures, and experimental conditions, with the intention to discriminate the basis for such colour effects.