Perception and mental representation of speech

Starting from theoretical considerations concerning fundamental linguistic and psychological aspects of research in perception and the mental representation o} speech, three experiments are presented. Employing a variety of experimental designs and methods and testing groups of subjects with different relevant characteristics, the experiments give evidence for a rejection of a featureand phoneme-oriented approach in the investigation of speech perception. Theoretical considerations This paper deals with aspects of psychophonetic problems of speech perception. Emphasis is laid on speech as a phenomenon which has psychological reality rather than on speech as a sociological factor in the sense of Saussure's langue'. This implies concern with the analysis of the behavior of language users in speech production and speech perception as can be investigated by applying physical and psychological methods. Alternative approaches dealing with speech from a sociological or formal perspective and governed by overall principles such as economy and formal simplicity lead to theoretical constructions, which — by aiming at something like an autonomous field of linguistics — deliberately neglect the actual behavior of language users. Such theoretical constructions appear as nothing but operational fictions with which the data they are supposedly based on can be handled and universal laws can be set up. Thus, the categories, structures, and systems which theoretically oriented linguists set up in their analyses of speech are not inherent in the language itself, but are products of the work of linguists dealing with their material. This contrast between an empirically founded versus a theoretical approach reminds one of the relation between phonetics and phonology Linguistics 27 (1989), 381-404 0024-3949/89/0027-0381 $2.00 © Mouton de Gruyter, Berlin 382 W. F. Sendlmeier in the 1930s. Although the representatives of structural phonology — especially those of the Prague school — were concerned with leaving aspects of perceptional psychology out of their theoretical concepts, they nevertheless were bound to refer to auditory judgments of acoustical phenomena in analyzing speech. These judgments were usually the product of their own subjective introspection. When within the field of phonology the distinctive-feature theory was introduced, the importance of auditory judgments for the description of acoustical features was stressed; however, the researchers did not verify the relation between stimuli and perceptual judgments by means of adequate phonetic experiments. In the field of generative phonology the relation between the acoustic stimulus and its human perceiver was neglected altogether, thus leading to the impossibility of empirically validating the theoretical constructs set up. When, in the early 1950s, phoneticians and psychologists working experimentally started to investigate the relation between the linguistic unit and its processing by the human listener, they were guided by the concept of minimal pairs and the ensuing distinctive-feature theory developed by phonologists. Thus they focused on the smallest isolated and reduced units — presented in the form of synthesized signals to listeners in the laboratory to be identified and discriminated. Notwithstanding the valuable results obtained by such studies, one should be aware of the fact that the experiments were based on artificial acoustic phenomena which were far removed from their natural manifestations. When preparing the stimuli in such a way that perception depends on nothing but the stimulus itself, one runs the risk of producing artefacts of the laboratory or else of simply registering in terms of psychophysics the aptitude of the peripheral acoustic analyzer and of neglecting the governing cognitive processes in speech perception. If one aims at discovering the nature of the perception process by the manipulation of external stimuli and of their presentation, one can never rule out for certain that by modifying the stimulus presentation, the character of the stimulus processing may also be affected. This uncertainty may be regarded as the psychological equivalent of Heisenberg's Unschärferelation, and I believe that this is one of the fundamental problems in perception research. In order to minimize this dilemma, it appears to be necessary to investigate the process of speech perception by means of widely varying methods. Among these there should be methods which aim at proving the sensitivity of the human listener to certain parameters within the acoustic signal as well as methods which, by starting from more complex natural units, help to gain insight into the human processing of speech and its presuppositions by means of a variety of tasks. Perception and mental representation 383 For the prevailing theories within phonology, words were and still are nothing but linked sounds. Although the phonological functions are manifested not in the sounds but in the words, and although sounds hardly ever occur in isolation but only as parts of words, the single sound became the objective of phonological analysis due to a viewpoint which might be characterized as 'atomistic' in spite of the fact that the researchers considered structures on the paradigmatic axis. Such an approach, however, can describe only part of the acoustic properties of words relevant for perception. Looking at the process of word recognition in everyday life situations, it becomes obvious that the listener — due to the situational context and strictly linguistic restrictions — does not consider all the words in his vocabulary alike as ones to be recognized. Instead, by interpretation of the existing restrictions, the listener arrives at a subset of his complete vocabulary which constitutes the frame for recognition. The process of identification and discrimination in word perception is strongly dependent on the size and type of such a subvocabulary. If this is so, generally valid statements about the relevance of certain phonetic features for the listener cannot be made, since the relevance of phonetic features varies with the relations between all the alternatives considered. Whether phonological oppositions, as they were deduced from minimal pairs, really do exist in the consciousness of the language user must be questioned. Given, first, that most words in a language have no direct partner with which to form a minimal pair, second, that in everyday life one is rarely confronted with the task of having to distinguish between two words constituting a minimal pair, and third, that words are formed as units and that differences between them are only later deduced and made consciously explicit (Oksaar 1977), it seems that the phenomenon of phonological opposition has been widely overestimated (see also Barry 1980). Ladefoged (1984) pinpoints the problem of the ontological status of phonemes even more closely when he writes, Perhaps the most startling conspiracy — one that seems to have deceived by far the majority of linguists — is the appearance of phonemes. Accounts of human behavior in terms of phonemes are nearly always examples of what has been called the psychologist's fallacy — the notion that because an act can be described in a given way that [sic] it is necessarily structured in that way. As far as I can see, phoneme size units play only a minor role in human behavioral acts such as normal speaking and listening (1984: 92; for further details see also Ladefoged 1980). The fact that the single sound and thus the concept of the phoneme stood and still stands so much in the center of phonetic-phonological approaches may certainly also be reduced to the fact that scientific 384 W. F. Sendlmeier perspectives are always culturally and biographically influenced. Most leading linguists came and come from an area where speech is represented by an alphabetic system. In their analyses they were concerned either with languages for which the same may be said or else with languages that had not been fixed in written form so that they could transfer their well-known principles without having to discuss competing writing systems. In contrast to such an approach, Firth (1957), for example — influenced by his work with languages transcribed on a syllabic basis — suggested a linguistic system for analysis and description in which suprasegmental and phonotactic phenomena play the central role. Unfortunately Firth never really developed a system that people not in contact with him could use (Kelly 1988); metrical and CV phonology are a welcome current development in a similar direction. It is widely known that a specific language background influences a person's ability to segment utterances, supporting the view that the single sound cannot be taken universally as the central perceptional unit. Language teachers report that Chinese speakers familiar only with the traditional logographic system have considerable difficulties with segmentation below word level; in contrast, Vietnamese, whose language is phonetically-phonologically somewhat similar to Chinese but has an alphabetic system, do not have the same kind of problems. Obviously previous experience concerning acoustical categorization influences the language user in his ability to arrive at phonetic-acoustical analyses of certain kinds. Teachers who teach adult illiterates confirm that their students often have great difficulties in segmenting the sound stream within the boundaries of words. Another possibility of gaining insight into the primary perceptual unit lies in looking at the early stages of a child's language-acquisition process. In first-language acquisition research, it has become a fact that the child learns a word as bearing meaning corresponding to a certain object or class of objects. It seems plausible to assume that in this learning process phonetic characteristics are globally perceived; in other words, the child learns, for example,