A major goal of psycholinguistics is to determine what sources of information are used immediately in language comprehension, and what sources come into play at later stages. Prepositional phrase attach-ment ambiguities were used in a self-paced reading task to compare contexts that contained one or two possible referents for the verb phrase (VP) in the target sentence. With one set of sentences, a VP-attachment preference was observed in the 2-VP-referent context, but not in the 1-VP-referent context. With another set of sentences, no effect of context was observed. This result falls outside of the scope of the principle of referential support (Altmann & Steedman, 1988) as currently formulated. It suggests that a similar but more broadly-based theory is required.

When a vertical test stimulus is presented simultaneously within a surrounding stimulus of orientation 10-30° clockwise from vertical, the test stimulus appears slightly counter-clockwise from vertical. In contrast, when the surrounding stimulus is 60-80° clockwise from vertical, the test stimulus appears slightly clockwise from vertical. Lateral inhibition between orientation-selective neurons can account for the former effect (repulsion), but not for the latter effect (attraction). H o w e v e r , if an orthogonal "virtual axis" is also present and exerts its o w n lateral inhibition, both effects can be accounted for. A mathematical m o d e l demonstrates quantitatively h o w this m a y occur in the visual system. O n e simulation with narrowly tuned orientation-selectivity functions produced tilt illusions of similar magnitude to that observed with h u m a n s at normal presentation durations. A simulation with m o r e broadly tuned functions produced tilt illusions of m u c h greater magnitude, as are found with h u m a n s at very short presentation durations. Based on the model's performance, h u m a n performance and neurophysiological data, it is suggested that: 1) lateral inhibition m a y be the immediate cause of both direct and indirect tilt illusions, and 2) the "virtual axis" m a y be a real neural mechanism and m a y be found in greater proportion in extrastriate cortex than in striate cortex.

We conducted sentence completion and eye-tracking reading experiments to examine the interaction of multiple constraints in the resolution of a lexical thematic ambiguity. The ambiguity was introduced with prepositional "by"-phrases in passive constructions, which can be ambiguous between agentive and locative interpretations (e.g., "built by the contractor" versus "built by the corner"). The temporarily ambiguous sentences were embedded in contexts that created expectations for one or the other interpretation. The constraints involved, including discourse-based expectations, verb biases, and contingent lexical frequencies, were independently quantified with a corpus analysis and a rating experiment. Our results indicate that there was an interaction of contextual and more local factors such that the effectiveness of the contexts was mediated by the local biases. Application of an explicit integration-competition model to the off-hne (sentence completion) and on-line (eye-tracking) results suggests that, during the processing of these ambiguous prepositional phrases, there was an immediate and simultaneous integration of the relevant constraints resulting in competition between partially active alternative interpretations.