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To briefly summarise what I have been reviewing so far: previous research spanning several decades has demonstrated that listeners encode talker-specific indexical information in their memo- ry representations, as manifested by what are typically referred to as indexical effects in spoken word processing. This realisation has motivated alternative views of speech perception and the lex- icon, wherein the memory representations of spoken words may be richer in content and more flex- ible than previously thought, comprising both linguistic and indexical information. However, it is yet unclear as to whether the integration of the abstract linguistic information with the more episod- ic indexical information takes place and is indeed stored within the lexicon. A better understanding of this issue is further complicated by inconsistencies in finding specificity effects across indexical studies, and the different approaches in the literature regarding the nature of the lexicon, with some of them going as far as questioning the need for such a specialised memory structure (e.g., Elman, 2004, 2009). Although the recent trend in the field favours hybrid models of spoken word recogni- tion and the lexicon, developing robust theoretical accounts and models remains a challenge for psycholinguistic theories of spoken word recognition.

Very recent evidence has suggested that spoken word processing seems to be also sensitive to speech-extrinsic auditory variability, manifested in a similar way to effects of indexical variabili- ty. To date, effects of such variability have been observed in tasks involving: implicit memory for the identification of highly filtered words, perceptual integration of indexical and speech-extrinsic auditory details (noise), and learning new words in the presence of background noise. The emer- gence of these effects has led to new claims regarding the nature of the lexicon, positing that be-

sides storing linguistic and indexical information, it could be further expanded to also include speech-extrinsic auditory details (Pufahl & Samuel, 2014).

The discovery of novel effects brings along excitement, but perhaps even more importantly, the need for further investigation. The research covered in this thesis was motivated by the recent speech-extrinsic specificity effects, in particular by the finding of Pufahl and Samuel (2014), to which I will refer to as the sound specificity effect henceforth. Before proposing a new view of the lexicon based on this effect, there are several critical questions about it that demand attention.

First, does the emergence of a sound specificity effect really entail the presence of the sounds in memory/lexicon alongside the words? Besides co-occurring with the words, the sounds also act as maskers, leading to degraded versions of them, alternatively known as acoustic glimpses. Two different sounds mask the same word differently, creating two distinct degraded versions of it. Ac- cordingly, the specificity effect could have been the result of the mismatch between the two distinct degraded versions of the same word in exposure and test, rather than due to the mismatch between the word-sound associations per se. This scenario would imply that it is not the word-sound associ- ations per se that are encoded in memory, but rather the degraded versions (glimpses) of the words as a result of masking from the sounds. Decoupling these two competing alternatives inspired the first research question explored in this thesis (Chapter 3).

Second, although observed under similar circumstances and methodology used to measure indexical effects, is the sound specificity really similar to the voice specificity effect? A spoken word is intrinsically different in nature from a word-sound pair. As described above, speech has an integral nature, wherein the linguistic and indexical component do not only co-exist, but are also integral to one another, belonging to the same perceptual object. On the other hand, the mere co- existence between words and sounds does not display this integrality element; the sounds can be perceptually segregated from the words with relative ease and the two do not belong to the same object. Does this discrepancy between the two stimuli types (words and word-sound pairs) con- strain the emergence of a sound specificity effect? In other words, is mere co-occurrence between words and sounds really sufficient to elicit a specificity effect? These questions were explored in Chapter 4.

Third, keeping with the indexical analogy, a spoken word is a unique utterance. No word is spoken in the same way across different speakers, and sometimes even by the same speaker. How would this uniqueness property translate to the co-existence of words and sounds in the investiga- tion of sound specificity effects? For instance, in Pufahl and Samuel (2014), the pairing between a word and a sound was unique, although they do not explicitly explain the reasons behind choosing to implement this association type in their stimuli. Does this element of the co-occurrence between 2 sounds and words play a role in the emergence of a sound specificity effect? Alternatively put, is an effect observed in that context replicable? This question is examined in Chapter 5.

These are the main arguments that motivated the present research, spanning several recogni- tion memory experiments and one implicit word identification study. Crucially, this thesis endorses both a comparative and explorative perspective in the investigation of sound specificity effects. The comparative aspect comes from the special attention dedicated to the analogy with indexical ef-

A word was paired with a unique sound exemplar, that was not used in another pairing.

fects, as well as frequent references made to the sound specificity effect found in Pufahl and Samuel (2014), in particular to its co-occurrence element. The explorative aspect lies in its attempts to identify plausible conditions that restrain or promote the emergence of sound specificity effects. In the section below, I briefly outline the organisation of the work in the remaining chapters.

1.8.1 The Present Research – Overview of the next chapters

In line with the rationale outlined above, the present research is organised along the follow- ing chapters:

♦ Chapter 2 is dedicated to the replication of the classical voice specificity effect, which serves as a comparative basis for the subsequent examination of the sound speci- ficity effect.

♦ Chapter 3 consists of three experiments that investigated the role of the acoustic glimpses of the same word(s) in the emergence of a sound specificity effect. In analogy to the two voices in the first experiment, two car horn sounds were used as pair companions of the spoken words.

♦ Chapter 4 will present two experiments that explored and identified the integrality factor between the word-sound associations as a necessary condition for the emergence of a sound specificity effect. A strict analogy to the voice specificity effect was endorsed, with a particular focus on the intrinsic relationship between words and voices.

♦ Chapter 5 involves two experiments (one being an extensive pilot for word intelli- gibility) that examined the role of pair-wise association uniqueness in the emergence of a sound specificity effect. In this case, association uniqueness refers to the unique pairing between a word and a sound. Since this part of the research also aimed at replicating the sound specificity effect originally reported by Pufahl and Samuel (2014), the same envi- ronmental sounds (a kind courtesy of April Pufahl) and a similar experimental design were used.

♦ Chapter 6 is the final chapter of the thesis and will provide a general discussion and concluding remarks of all the results described in the previous chapters.