The Loci of Age of Acquisition and Word Frequency Effects: Evidence From Contemporary Experimental Paradigms and Eye-Tracking.

Previous research has demonstrated that earlier acquired and frequently occurring words and concepts are processed significantly faster and more accurately than their later acquired and infrequently occurring counterparts. These effects have been observed across samples, languages, stimuli sets and experimental paradigms; suggesting that the phenomena are valid and reliable. However, a number of methodological limitations are evident in the literature and these issues have hindered attempts to identify the nature and loci of these effects. These limitations were subsequently addressed in this thesis. This enabled the researcher to investigate the effects of age-of-acquisition (AoA) and word frequency during perceptual processing, semantic processing, indirect lexical access, direct lexical access, lexical retrieval and articulation. The programme of research outlined in Chapter 2 consisted of a systematic series of laboratory experiments which each assessed different aspects of cognitive processing. Standardised, semi-factorial stimuli sets were also designed and implemented throughout this programme of research to improve validity. Furthermore, methodological and analytical elements were controlled across the experimental paradigms to ensure reliability and facilitate the comparison of AoA effects across levels of processing. Chapters 3 – 8 report six studies consisting of twelve semi-factorial experiments in which the effects of AoA and word frequency were investigated during perceptual identification, picture-category verification/falsification, picture-name verification/falsification, immediate picture naming task, immediate word reading task and delayed picture naming. These experiments revealed that AoA exerted significant, strong and consistent effects on processing speed across all of the experimental paradigms reported in this thesis when word frequency, imageability, concreteness, familiarity, visual complexity, orthographic neighbourhood density, picture-name agreement and word length were controlled. However, word frequency did not exert a consistent, significant effect when AoA, imageability, concreteness, familiarity, visual complexity, orthographic neighbourhood density, picture-name agreement and word length were controlled. Therefore, AoA effects were independent of word frequency effects. Chapter 9 reports a comparison of the AoA effects which were observed across these experimental paradigms. This chapter indicates that while AoA influenced all levels of processing, the effects were strongest during tasks which required indirect lexical access and arbitrary mapping between levels of representation. These findings lend considerable support to the multi-loci perspective and dispute both the Phonological Completeness Hypothesis (PCH) and the Semantic Hypothesis (SH). Indeed, AoA is a prominent factor which plays a pivotal role in determining processing speed throughout cognitive system rather than solely during one level of processing. Based on the evidence reported in this thesis, the researcher subsequently argues in Chapter 10 that there is at least one, strong locus of AoA effects which occurs during semantic-lexical encoding and at least one weaker locus which occurs during perceptual-semantic encoding.