Using word frequency and parafoveal preview to determine the locus of contextual predictability and imageability effects evidence from eye movements during reading and lexical decision
The present thesis examines the time course of two semantic variables, contextual predictability and word imageability. Both variables can be said to reflect semantic aspects of meaning. For example the contextual predictability of a given target indicates the semantic context within which the target word occurs. The imageability of a given word reflects the meaning aspects of the word itself (Whaley, 1978) The word frequency effect (the faster response to commonly used high frequency words compared to low frequency words which occur less often) was taken to index the moment of lexical access (Balota, 1990; Pollatsek Rayner, 1990; Sereno Rayner, 2003) and by applying the logic of additive factors method (Sternberg, 1969a, 1969b) we determined whether the combined effect of each respective semantic variable was additive or interactive. This allowed us to examine whether there are semantic influences on lexical access. Previous research has been undecided and the question remains as to whether semantic variables operate during the lexical access processing stage, or alternatively after lexical access, for example in the post lexical stage (e.g. Hand, Miellet, Sereno O'Donnell, 2010; Sereno, O'Donnell Rayner, 2006) Another aim of the thesis was to address the issue concerning the information presented to participants in the condition of 'invalid parafoveal preview of a target' (e.g. Sereno Rayner, 2000) Several criteria were identified as being important in order to make the assumption that parafoveal processing was successfully inhibited on the pre target fixation. Another aim of the thesis was to investigate whether word frequency and contextual predictability of the parafoveal word affected parafoveal preview benefit. Preview benefit was calculated by subtracting fixation durations in a condition of 'valid' preview of the target with an 'invalid' preview of the target. Experiment 1 utilised a lexical decision task to investigate the relationship between word frequency and the imageability of the word. Experiment 2 investigated whether the orthogonal manipulation of word frequency and contextual predictability led to an additive or interactive relationship between these two variables. Two pre tests, the rating and Cloze tasks, were used to determine the predictability of the target. Experiment 3 and a further cross comparison of Experiments 2 and 3 replicated and extended Experiment 2 by additionally using an eye movement contingent boundary change paradigm (Rayner, 1975) Experiment 4 examined the joint and combined effects of frequency, predictability and preview in a within subjects design. A separate pre test Cloze task was used to determine predictability of targets in their low and high predictable contexts. This experiment used a larger set of materials than in the previous experiments to examine these variables. Finally Chapter 6 was an overall discussion of the thesis. It was concluded that display screen presentations in our eye tracking experiments led to very fast reading times (as well as more skipping) compared to past studies which have used dot matrix display presentations. It is possible that faster fixation durations led to floor effects in conditions where reading times are already fast because of preferential circumstances of high frequency targets, high predictable contexts and being given a parafoveal preview of the target. Possible ways to counteract this floor effect as well as alternative experimental methods of investigation were discussed.