Psychology and Religion

[Vexari]

The language machine: Psycholinguistics in review.


Gerry T. M. Altmann

Psycholinguistics is the empirical and theoretical study of the mental faculty that underpins our consummate linguistic agility. This review takes a broad look at how the field has developed, from the turn of the 20th century through to the turn of the 21st. Since the linguistic revolution of the mid-1960s, the field has broadened to encompass a wide range of topics and disciplines. A selection of these is reviewed here, starting with a brief overview of the origins of psycholinguistics. More detailed sections describe the language abilities of newborn infants; infants' later abilities as they acquire their first words and develop their first grammatical skills; the representation and access of words (both spoken and written) in the mental lexicon; the representations and processes implicated in sentence processing and discourse comprehension; and finally, the manner in which, as we speak, we produce words and sentences. Psycholinguistics is as much about the study of the human mind itself as it is about the study of that mind's ability to communicate and comprehend.

By degrees I made a discovery of still greater moment. I found that these people possessed a method of communicating their experience and feelings to one another by articulate sounds. I perceived that the words they spoke sometimes produced pleasure or pain, smiles or sadness, in the minds and countenances of the hearers. This was indeed a godlike science, and I ardently desired to become acquainted with it.

Mary Shelley Frankenstein, or, the modern Prometheus (Penguin edition, p. 108)

Through language we each of us cut through the barriers of our own personal existence. In doing so, we use language as an abstraction of the world within and around us. Our ability to interpret that world is extraordinary enough, but our ability to abstract from it just certain key aspects, and to convey that abstraction through the medium of language to another individual, is even more extraordinary. The challenge for psychology has been to reveal, in the face of extraordinary complexity, something of the mental representations and processes that underpin our faculty for language. The purpose of this review is to convey those aspects of psycholinguistic research that have shaped the current state-of-the-art. The reader should bear in mind, however, that the Handbook of psycholinguistics (Gernsbacher, 1994) contains in excess of 1100 pages and a subject index with barely fewer words than the number originally suggested for, but subsequently exceeded by, this review. The full depth, richness and scope of psych olinguistics thus goes far beyond the limits afforded here.

Psycholinguistics boomed (as did the rest of psychology) in the early to mid-1960s. The Chomskian revolution (e.g. Chomsky, 1957, 1965, 1968) promoted language, and specifically its structures, as obeying laws and principles in much the same way as, say, chemical structures do. The legacy of the first 50 or so years of the 20th century was the study of language as an entity that could be studied independently of the machinery that produced it, the purpose that it served, or the world within which it was acquired and subsequently used. The philosopher Bertrand Russell (1959) was sensitive to this emerging legacy when he wrote: 'The linguistic philosophy, which cares only about language, and not about the world, is like the boy who preferred the clock without the pendulum because, although it no longer told the time, it went more easily than before and at a more exhilarating pace.' Subsequently, psycholinguistic research has nonetheless recognized the inseparability of language from its underlying mental machi nery and the external world.

The review begins with some brief comments on the early days of psycholinguistics (including both early and current British influences on the field). It then moves to a selection of current topics in psycholinguistics, beginning with the language abilities of newborn infants, and moving on from how infants represent the speech they hear to how they acquire a first vocabulary and how later, as adults, they represent and access words in the mental lexicon (both spoken and written). From there, we move on to the acquisition of grammatical skills in children and the processing of sentences by adults and to text and discourse understanding. The article then considers how adults produce, rather than comprehend, language, and ends with a brief overview of some of the topics that are not covered in-depth in this review.


Psycholinguistics: the early days

Psycholinguistics is, as Wilhelm Wundt (1832-1920) noted in Die Sprache (1900), as much about the mind as it is about language. All the more paradoxical, then, that perhaps the earliest use of the term 'psycholinguistics' was in J. R. Kantor's Objective psychology of grammar (1936), in which Kantor, an ardent behaviourist, attempted to refute the idea that language reflected any form of internal cognition or mind. According to Kantor, the German psycholinguistic tradition was simply wrong. The term became more firmly established with the publication in 1954 of a report of a working group on the relationship between linguistics and psychology entitled Psycholinguistics: A survey of theory and research problems (Osgood & Sebeok, 1954/1965); the report was published simultaneously in two journals that, separately, served the linguistics and psychology disciplines. Almost 50 years on, research into the many different aspects of the psychology of language is now published in a vast range of journals, and accounts for around 10% of all publications in psychology, [1] a figure that has remained remarkably constant given the approximately fivefold increase in the annual publication rate across psychology as a whole since the 1950s.

Psycholinguistics suffered a turbulent history during the first part of the 20th century, not least because of the behaviourist movement. Even William James, who foresaw many psycholinguistic issues in his The principles of psychology (1980, 1950), had turned his back on Wundtian psychology at the very end of the 19th century. Blumenthal (1970), in his historical overview of the early years (and on which parts of this section are based), described psycholinguistics in the early to mid-20th century as the study, in the West at least, of verbal learning and verbal behaviour--a reflection of the behaviourist approach to language learning (the more mentalist approach advocated by Wundt still prevailed in German, and to an extent Soviet, psychology during that time). Within linguistics, the Bloomfieldian school was born (with Bloomfield's Language published in 1933) which, although acknowledging the behaviourist endeavour within psychology, promoted the study of language independently of psychology, and took to t he limits the taxonomic approach to language. Notwithstanding the behaviourist backdrop, a significant number of empirical studies reported phenomena in those early days that still predominate today (mostly on reading or speech perception; e.g. Bagley, 1900; Cattell, 1886; Dodge & Cline, 1915; Huey, 1900, 1901; Pillsbury, 1915; Pringle-Morgan, 1896; Stroop, 1935; Tinker, 1946). Theoretically, the field moved on (or at least, should have done) following Karl Lashley's (1951) article on serial order in behaviour. Despite no reference to Wundt, there were considerable similarities with the Wundtian tradition. Specifically, Lashley sought to show that the sequential form of an utterance is nor directly related to the syntax of that utterance (a theme to be found in Wundt's writings, and later taken up by the Chomskian school), and that (partly in consequence) the production of an utterance could nor simply be a matter of complex stimulus-response chains as the behaviourist movement would have it. Skinner, in his Verbal behaviour (1957), took on-board some of these limitations of behaviourism when, despite advocating that psychology abandon the mind, he argued for a system of internal mediating events to explain some of the phenomena that the conditioning of verbal responses could not explain. The introduction of such mediated events into behaviourist theory led to the emergence of neo-behaviorism, most notably associated, within language, with Charles Osgood.

The year 1957 was something of a watershed for psycholinguistics, not because of the publication of Verbal behaviour, but because of the publication of Chomsky's Syntactic structures (1957)--a monograph devoted to exploring the notion of grammatical rules. Subsequently, in his review of Skinner's Verbal behaviour, Chomsky (1959) laid to rest the behaviourist enterprise (at least as it applied to language). Space precludes the breadth of argument, but crudely speaking no amount of conditioned stimulus-to-verbal-response associations could explain the infinite productivity (and systematicity) of language. With Chomsky, out went Bloomfield, and in came mental structures, ripe for theoretical and empirical investigation. Chomsky's influence on psycholinguistics, let alone linguistics, cannot be overstated. Although there have been many critics, specifically with regard to his beliefs regarding the acquisition of grammar (see under 'From words to sentences below), there is little doubt that Chomsky reintroduced t he mind, and specifically mental representation, into theories of language (although his beliefs did not amount to a theory of psychological process, but to an account of linguistic structure). Indeed, this was the sticking point between Chomsky and Skinner: Skinner ostensibly eschewed mental representations, and Chomsky proved that language was founded on precisely such representation. Some commentators (e.g. Elman et al., 1996) take the view, albeit tacitly, that the Chomskian revolution threw out the associationist baby with the behaviourist bathwater. Behaviourism was 'out', and with it associationism also. Symbolic computation was 'in', but with it, uncertainty over how the symbolic system was acquired (see under 'From words to sentences' below). It was not until the mid-1980s that a new kind of revolution took place, in which the associationist baby, now grown up, was brought back into the fold.

In 1986 Rumelhart and McClelland published Parallel distributed processing (1986b; see Anderson & Rosenfeld, 1998, for an oral history of the topic, and R. Ellis & Humphreys, 1999, for an explanation and examples of its application within psychology). This edited volume described a range of connectionist, or neural network, models of learning and cognition. [2] 'Knowledge' in connectionist networks is encoded as patterns of connectivity distributed across neural-like units, and 'processing' is manifest as spreading patterns of activation between the units. These networks can learn complex associative relations largely on the basis of simple associative learning principles (e.g. Hebb, 1949). Importantly, and in contrast to the ideals of the behaviourist traditions, they develop internal representations (see under 'From words to sentences' below). The original foundations for this paradigm had been laid by McCulloch and Pitts (1943) and further developed by Rosenblatt (1958). Rumelhart and McClelland's collect ion marked a 'coming of age' for connectionism, although many papers had already been published within the paradigm. One of the most influential models in this mould was described by Elman (1990; and see M. I. Jordan, 1986, for a precursor), who showed how a particular kind of network could learn the dependencies that constrain the sequential ordering of elements (e.g. phonemes or words) through time; it also developed internal representations that appeared to resemble grammatical knowledge. Not surprisingly, the entire enterprise came under intense critical scrutiny from the linguistics and philosophy communities (see e.g. Marcus, 1998a, 1998b; Pinker & Mehler, 1988), not least because it appeared to reduce language to a system of statistical patterns, was fundamentally associationist, and eschewed the explicit manipulation of symbolic structures: the internal representations that emerged as a result of the learning process were not symbolic in the traditional sense.

Critics notwithstanding, statistical approaches to language (both in respect of its structure and its mental processing) are becoming more prevalent, with application to issues as diverse as the 'discovery' of words through the segmentation of the speech input (e.g. Brent, 1999; Brent & Cartwright, 1996), the emergence of grammatical categories (Elman, 1990), and even the emergence of meaning as a consequence of statistical dependencies between a word and its context (e.g. Burgess & Lund, 1997; Elman, 1990). Empirically also, the statistical approach has led to investigation of issues ranging from infants' abilities to segment speech (Saffran, Aslin, & Newport, 1999) and induce grammar-like rules (Gomez & Gerken 1999, 2000) to adult sentence processing (MacDonald, 1993, 1994; MacDonald, Pearlmutter, & Seidenberg, 1994a; Trueswell, 1996; Trueswell, Tanenhaus, & Kello, 1993).

This is where we are now. There is no doubt that connectionism has had a profound influence on psycholinguistic research and cognitive psychology more generally. But despite its attractions (for some at least), it would be disingenuous to ignore the insights and historical convergence among the other disciplines within psychology, linguistics and philosophy that have brought us this far, and which will, like connectionism, take us further.

In the 100 years that have passed since the inception of the British Psychological Society, psycholinguistics has developed into a fully fledged scientific discipline. It is appropriate, in the context of this anniversary issue of the British Journal of Psychology, to draw attention to the British influence on that development--an influence that continues to pervade the field. Specific examples of how topics within the field owe their development in major part to British researchers include Morton's and subsequently Marslen-Wilson and Tyler's influence on the development of models of lexical process and representation (concerning the access and organization of the mental dictionary); Cutler and Norris's work on prelexical segmentation processes (the breaking down of the spoken input into representational units that are relevant for lexical access); Mitchell's work on, among other things, language-specific constraints on syntactic processing, and Steedman and Altmann's work on contextual constraints on such p rocessing; Johnson-Laird's influence on the development of 'mental models' (representations of text and discourse); Sanford and Garrod's, and Garnham's, work on inferential processing and referential continuity during text processing (the inferences and representations that enable the hearer/reader to interpret the dependence between an expression in one part of the text and earlier parts of the text); Bryant, Goswami and others on reading and its development; Snowling, Oakhill, Frith and Bishop on disorders of reading and of language more generally (including disorders associated with dyslexia, autism and specific language impairment); Marshall, Shallice, Warrington, and A. W. Ellis on the neuropsychology of language breakdown (following brain injury); and other researchers too numerous to mention, but each of whom has played a significant part in the development of the field as it stands today. The following sections review that field. However, given that it is often difficult to disentangle British influen ces on psycholinguistics from the other international influences that have contributed to its progress, no attempt is made to do so explicitly in the review that follows.


Language and infancy

It is in utero that the foundations are most commonly laid for subsequent language learning and adult language use. It was established in the 1980s that perhaps the first linguistic variation to which newborn babies are sensitive is prosody (variation in the pitch, intensity and duration of the sounds of speech--the melody, so to speak). Babies appear to learn the prosodic characteristics of 'material' they hear in utero. DeCasper and colleagues (e.g. Cooper & Aslin, 1989; DeCasper, Lecanuet, Busnel, Granier-Deferre, & Maugeais, 1994; DeCasper & Spence, 1986) demonstrated that newborns recognize--indeed prefer--the prosodic characteristics of the maternal voice, as well as the characteristics of particular rhymes spoken repeatedly by the mother during the last weeks of pregnancy. Mehler et al. (1988) demonstrated that newborn babies recognize, more generally, the prosodic 'signature' of their mother tongue, even though they have yet to learn the segmental characteristics of their maternal language (the specif ic sounds, and their combinations, that define the words in the language). Thus, aspects of language can be learned in utero and without a 'semantics'; it is not necessary for linguistic variation to map onto meaning for that variation to be learned, even though the greater part of language learning is concerned with establishing precisely such a mapping.

The newborn baby is armed, however, with more than just an appreciation of the prosodic characteristics of what will probably become its mother tongue. It is armed also with an ability to recognize, in a particular way, the individual sounds of the language (the phonemes) which, combined in different ways, give rise to the words of the language. Liberman, Harris, Hoffman, and Griffith (1957) demonstrated that phonemes are perceived categorically--despite an almost infinite range of sounds that could make up the dimension along which the initial phonemes of the words 'buy' and 'pie' vary, we appear to perceive just two phonemes; /b/ and /p/. Eimas, Siqueland, Jusczyk, and Vigorito (1971) demonstrated that this mode of perception is not learned, but is present in young infants, and Bertoncini, Bijeljac-Babic, Blumstein, and Mehler (1987) demonstrated subsequently that it is present even in newborns (and see Nakisa & Plunkett, 1998, for a computational account based on a genetic learning algorithm). And althoug h nor all languages use the same categories within a given dimension (Thai, for example, has an extra phoneme where we only have /b/ and /p/), babies appear sensitive to all used categories (e.g. Lasky, Syrdal-Lasky, & Klein, 1975; Streeter, 1976) until around 8-10 months, by which time they have lost their earlier sensitivity to categories that are nor relevant within their own language (e.g. Werker & Lalonde, 1988; Werker & Tees, 1984). Our perception of these categories is modulated by a variety of influences: for example, Ganong (1980) demonstrated that if a segment that is ambiguous between /b/ and /p/ replaces the final segment of the word 'clap' it will tend to be perceived as /p/, but the same acoustic token at the end of 'blab' will be perceived as /b/ Also Summerfield (1981) demonstrated that the perceived rate of speech modulates perception--the /p/ uttered in 'pie' (spoken quickly) could be acoustically identical to the /b/ uttered in 'buy' (spoken normally); and yet we would still perceive the fi rst word as 'pie'. Infant perception is also modulated in this way (e.g. Miller & Eimas, 1983). Thus, our interpretation of the acoustic input is determined by our interpretation (at a variety of different levels of analysis) of the surrounding input.

Liberman et al.'s (1957) original observation was partly responsible for the idea that the manner in which we perceive speech is uniquely human and quite speech-specific. For a time, it was believed that there existed phoneme detectors that operated in much the same way as motion detectors (e.g. they could he 'fatigued'; Eimas & Corbit, 1973; but see Ades, 1974, for evidence against position-independent phoneme detectors). However, it since transpired that many of these effects are not confined to human perceivers: a range of other species perceive phonemes categorically (e.g. Kuhl & Miller, 1975), with their perception also modulated by speech rate (Stevens, Kuhl, & Padden, 1988). The precise mechanism that brings about the appearance of discontinuous perception is the subject of some considerable controversy: Massaro (1987, 1994) has pointed our that perception could be continuous hut that the application of a decision rule (operating preconsciously) would lead naturally to the appearance of discontinuiti es in the appropriate identification and discrimination functions. Nonetheless, it would appear that the newborn infant brings with it into the world a perceptual mechanism that is neither specific to humans nor to speech, but which endows it with some considerable advantage. A problem for the infant is to know that different instances of the same word are the same word; categorical perception may provide the infant with a solution to that problem.

The relevance of these observations on prosodic sensitivity and discontinuous perception of phonemes concerns the nature of the mental representations that are constructed on the basis of the novel input that the newborn encounters. Newborns apparently recognize what they hear in terms of syllabic units, and anything that is not a 'legal' syllable is neither recognized nor distinguished in the same way (e.g. Bertoncini & Mehler, 1981; Mehler, Dupoux, & Segui, 1990). Only legal syllables have the prosodic characteristics that the infant is already familiar with, and the infant therefore recognizes syllables through recognizing familiar prosodic patterns. Presumably, the infant subsequently can categorize these familiar patterns in terms of their phonemic content also.

To conclude: the newborn infant is set up to organize what it hears in linguistically relevant ways, as if it were born to recognize the building blocks of the words it will learn subsequently. This ability need not be based on some innate, language-specific mechanism, but need only be based on a mechanism, perhaps statistical in nature, with which to learn the prosodic tunes of the language (a statistical regularity in its environment), and on a mechanism shared with other species with which to identify and discriminate finer segmental information in the face of linguistically irrelevant variation. [3] For the infant, language is not an independent entity divorced from the environment in which it is produced and comprehended; it is a part of that environment, and its processing utilizes mental procedures that may not have evolved solely for linguistic purposes.


Contacting the lexicon I: spoken word recognition

The importance of a syllabic basis to early linguistic representations pervades the literature on lexical access--the manner in which the mental representations of the words in the language are accessed. In the early 1980s, research on English and French established syllable-bounded representations as central to the access process (e.g. Cutler, Mehler, Norris, & Segui, 1986; Mehler, Domergues, Frauenfelder, & Segui, 1981); the syllabic structure of the maternal language apparently could influence the nature of the representations that 'contact' the mental lexicon following auditory input. Thus, French has a syllabic structure (and indeed, a prosodic structure) that is different in significant ways from English, and similarly for languages such as Spanish, Catalan or Japanese (cf. Otake, Harano, Cutler, & Mehler, 1993; Sebastian-Galles, Dupoux, Segui, & Mehler, 1992). How these representations, as reactions to the speech input, develop from infancy onwards has only recently been explored (see Jusczyk, 1997, fo r a review). But all the indications are that the prosodic/syllabic attributes of the language being learned have a fundamental influence on the sensitivities of the infant, as do statistical regularities in the language (see Jusczyk, 1999, for a review; and Saffran et al., 1999, for an empirical demonstration of statistical learning in infants). The infant language device is, again, a product of the environment in which it finds itself, and appears to be at the mercy of the statistical regularities within that environment.


Learning words

The task for the infant as it begins to acquire a lexicon, and learn the meanings of words, is by no means simple (see Bloom, 2000, for a recent review on word learning): how are children to know which of the many sounds they hear correspond to which of the infinite range of possibilities before them? For example, children may be able to work out that, among the sounds in the spoken utterance 'look, the dog's playing with a ball', the sounds corresponding to 'dog' are intended to correspond to the animal in front of them (perhaps because they already know that 'ball' refers to the ball, and have a sufficient grasp of syntax to realize that 'dog' is a noun and will hence refer to something). But children must still work out whether 'dog' corresponds to the concept associated with dogs, or with animals more generally; or to things of that shape, or to things of that colour; or to its head, or to all of it. Given the infinite number of hypotheses that children might test (Quine, 1960) how are they to…

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