The aim of this PhD thesis was to investigate the interaction between spatial attention mechanisms and English words, when participants are undertaking variations of the letter search (LS) task. In Section 1 the LS task is investigated through manipulating some of the main dimensions upon which LS tasks differ in the published literature. The results reported here add to the current understanding of LS tasks, and extend the knowledge of the effects sometimes subtle manipulations can have. The set of experiments in Section 2 investigates the effect of focussing attention on single letters presented on their own, in letter strings, and in real words. The manipulations of perceptual load and predictability of target location, allow for the testing of the common assumptions about the way items are selected within words. The mechanisms involved in selection are suggested to be interplay between inhibitory and excitatory systems. Finally, in Section 3, the effect of searching for a letter in a
word on the semantic priming is examined. The final section concentrates on target letter position effects and positive and negative search. The evidence from the last experiment has implications for the way that prime task effect experiments are constructed, and for models of semantic memory and visual word recognition.