System-level attention links cognition, perception and action: Evidence from language comprehension and eye movements

The research reported in this thesis attempted to establish the underlying representational substrate within which cognition, perception and action interact. A theoretical framework was adopted in which attention functions at a system level as the mediating mechanism between cognitive functions and sensorimotor responses. This was achieved by addressing two issues: a) whether representations activated by language comprehension can compete with representations involved in eye movement control; and b) whether this competition creates attentional conflict within the system and thus modulates the oculomotor response. The effects of two types of words, directional verbs and locational nouns, on two types of eye movements, pursuit and saccades, were explored in nine eye-tracking experiments. Empirical findings suggested that a) eye velocity during pursuit was systematically modulated by verb semantics; depending on whether there was agreement or conflict between representations activated by the directional verbs and the oculomotor task, eye velocity was respectively increased or decreased; b) saccadic launch latency was consistently modified by verb semantics; saccades were initiated with reduced or increased latencies when representations involved in language comprehension and eye movement control were in accordance or in conflict with each other. This collection of evidence points to a unified, attention-governed system that encompasses cognition, perception and action.