Trace (psycholinguistics) Totally Explained

Everything about Trace Psycholinguistics totally explained

TRACE is a Connectionist model of speech perception, proposed by James McClelland and Jeffrey Elman in 1986. TRACE was made into a working computer program for running perceptual simulations. These simulations are predictions about how a human mind/brain processes speech sounds and words as they're heard in real time.

Inspiration

TRACE was created during the formative period of Connectionism, and was included as a chapter in "". The researchers found that certain problems regarding speech perception could be conceptualized in terms of a Connectionist interactive activation model. The problems were that (1) speech is extended in time, (2) the sounds of speech (phonemes) overlap with each other, (3) the articulation of a speech sound is affected by the sounds that come before and after it, and (4) there's natural variability in speech (for example foreign accent) as well as noise in the environment (for example busy restaurant). Each of these causes the speech signal to be complex and often ambiguous, making it difficult for the human mind/brain to decide what words it's really hearing. In very simple terms, an interactive activation model solves this problem by placing different kinds of processing units (phonemes, words) in isolated layers, allowing activated units to pass information between layers, and having units within layers compete with one another, until the “winner” is considered “recognized” by the model.

Key findings

A simulation of speech perception involves presenting the TRACE computer program with mock speech input, running the program, and generating a result. A successful simulation indicates that the result is found to be meaningfully similar to how people process speech. To use an analogy, a model of the stock market is a theory about how the market works. If the model is made into a computer program and the program generates a one-year forecast of market performance, then that's a testable prediction. If the prediction turns out to be completely accurate, then the model must be a useful theory about the stock market. TRACE is the same kind of theory, only it's interested in how people perceive speech.

Time-course of word recognition

It is widely accepted in psycholinguistics that (1) when the beginning of a word is heard, a set of words that share the same initial sound become activated in memory, (2) the words that are activated compete with each other while more and more of the word is heard, (3) at some point, due to both the auditory input and the lexical competition, one word is recognized. TRACE reliably simulates this, and can explain it in relatively simple terms. Essentially, the lexical unit which has become activated by the input (for example wood) feeds back activation to the phoneme layer, boosting the activation of it’s constituent phonemes (for example /d/), thus resolving the ambiguity.

Lexical basis of segmentation

Speakers don't leave pauses in between words when speaking a sentence, yet people seem to have no difficulty hearing sentences as a sequence of words. This is known as the segmentation problem, and is one of the oldest problems in the psychology of language. TRACE proposed the following solution, backed up by simulations. When words become activated and recognized, this reveals the location of word boundaries. Stronger word activation leads to greater confidence about word boundaries, which informs the hearer of where to expect the next word to begin. While it shares a number of features with TRACE, a key difference is the following. While TRACE permits word units to feed back activation to the phoneme level, Merge restricts its processing to feed-forward connections. In the terms of this debate, TRACE is considered to violate the principle of information encapsulation, central to modularity, when it permits a later stage of processing (words) to send information to an earlier stage (phonemes). Merge advocates for modularity by arguing that the same class of perceptual phenomena that's accounted for in TRACE can be explained in a Connectionist architecture that does not include feedback connections. Norris et al. point out that when two theories can explain the same phenomenon, parsimony dictates that the simpler theory is preferable.

Applications

Speech and Language Therapy

Models of language processing can be used to conceptualize the nature of impairment in persons with speech and language disorder. For example, it has been suggested that language deficits in Broca's aphasia may be caused by excessive competition between lexical units, thus preventing any word from becoming sufficiently activated. Arguments for this hypothesis consider that mental dysfunction can be explained by slight perturbation of the network model's processing. This emerging line of research incorporates a wide range of theories and models, and TRACE represents just one piece of a growing puzzle.

Distinction from speech recognition software

Psycholinguistic models of speech perception, for example TRACE, must be distinguished from computer speech recognition tools. The former are psychological theories about how the human mind/brain processes information. The latter are engineered solutions for converting an acoustic signal into text. Historically, the two fields have had little contact, but this is beginning to change.

Influence

TRACE’s influence in the psychology literature can be assessed by the number of articles that cite it. There are 345 citations of McClelland and Elman (1986) in the PsycINFO database. Figure 3 shows the distribution of those citations over the years since publication. The figure suggests that interest in TRACE grew significantly in 2001, and has remained strong, with about 30 citations per year.

Further Information

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