Induction explained?

lateral prefrontal and parietal cortex. The authors suggest that the time course of the changes observed indicate that the ventral striatum is more likely to be involved in the detection of novelty, while the right prefrontal cortex is more likely to be involved in the maintenance of contextual information. It is important to note that both the striatal and prefrontal activations occurred without conscious awareness. These findings therefore question current theories of prefrontal function that stress a role in the active, conscious maintenance of information because the subjects in this experiment were unaware of the ordered sequences used and therefore had no conscious reason to maintain the identity of previous stimuli or responses.

Novelty detection in the absence of conscious awareness The detection of novelty is a complex cognitive process that is fundamental to survival. Clearly an event can be novel in one situation but not in another. However, the study of novelty is often confounded by concurrent awareness because novel events are often very salient and therefore capture attention and awareness. In a interesting departure from the norm, the processes governing the detection of novelty were investigated by Berns et a/. in a recent study incorporating positron emission tomography and an implicit learning task. Subjects were scanned while they performed a serial reaction-time task in which they observed sequences of visual stimuli and had to press a key pad after each stim-

ulus. Although the subjects were unaware that the stimuli repeated in a fixed order, their reaction times decreased with practice, indicating that the subjects had learned about the sequence order in the absence of awareness. Thus, implicit learning was established. Once the subjects were trained on one sequence, a small and unperceived change in the sequence order was instigated. Comparisons between the scans obtained during the performance of the old and new sequences revealed that the change enhanced cerebral blood flow in a network of structures including the left premotor area and anterior cingulate, and the right ventral striatum. Decreased blood flow was observed in the right dorso-

Reference Bernr,

G.S. et al. (1997)

to novelty

Brain

in the absence

regions

responsive

of awareness

Science

276, 1272-1275

-

Induction

Imaging language in Broca’s area

explained?

A paradoxical problem that has engaged the minds of the most eminent philosophers, psychologists and cognitive scientists for many years, is that we appear to be able to extract a much larger amount of knowledge from a given amount of information, than appears to have been present within that information. For example, according to Landauer and Dumais’, it has been calculated that a young child acquires the meaning of 10 to 15 new words every day. They suggest that most are acquired through reading because the majority of English words are used only in print and most of those encountered in speech are already known. Although approximately one word is taught directly each day*, only about three words are acquired through reading because the average child reads only 50 paragraphs a day, but only learns the meaning of one new word every 20 paragraphs (see Refr 1,3.4). Therefore for Landauer and Dumais, the paradox relates to how we learn the meaning of the additional 6 to 11 words. They suggest that Plato resolved the paradox by assuming that we are born with most of our knowledge and that we need only some hints and enough time to conlemplate to complete it. Perhaps more famously, Chomsky and others have suggested that language acquisition is based on a set of innate general rules that are applied, rather than acquired, to facilitate language acquisition. However, recent work by Landauer and Dumais (1997) challenges these ideas by describing a novel general theory of acquired similarity and knowledge representation, latent semantic analysis (LSA). This high-dimensional linear associative model embodies no human knowledge

beyond its general learning mechanism and was used on a large body of text to generate a representation that captured the similarity of words and text passages. The knowledge acquired during this training phase was then tested with a standard mutiple-choice synonym test and the results were compared with the rate at which school-age children improve their performance on similar tests as a result of reading. The model’s improvement rate was similar to that observed in school children and most of the acquired knowledge was attributed to direct inference, rather than direct cooccurrence relationships. The authors conclude that this demonstration questions the requirement for an innate foundation for language acquisition and may therefore challenge current theories concerning the acquisition of human knowledge. If substantiated, these findings may have profound implications for the future study of philosophy, artificial intelligence and psychology in addition to their linguistic implications. References 1 Landauer,

T.K.

solution

to Plato’s

analysis

theory

representation

and

Dumais,

problem: of

S.T. (1997)

the latent

acquisition,

of knowledge

A

semantic

induction, Psycho/.

and

Rev. 104,

211-240 2

Durkin,

vations

D. reveal

instruction

(1979)

What

about

reading

Reading

classroom

Research

obrer-

comprehension Quarter/y

14,

481-523 3 Carver, of reading

R.P. and Leibert, library

difficulty

upon

Research

Quarterly

4 Carver, Research

books

gain

R.E. (1995) The effect at different

in reading

levels

ability

of

Reading

Reference

30, 2648

Kim,

R. P. (1990) Reading and Theory.

Academic

Copyright Trends

Topographic specialization of language processing in multilingual subjects has been suggested by clinical reports of patients who show selective impairments in one or more languages following surgery, partial seizure or electrical stimulation of discrete cortical areas. Kim et al. now extend this work by illustrating the existence of spatially separate cortical areas for each language in bilingual subjects using functional magnetic resonance imaging (fMRI). Subjects were required to perform silent, internally expressive, linguistic tasks in two different languages Two distinct, but adjacent areas of activation were observed within Broca’s area (Brodmann’s area 44) in those subjects who had acquired conversational fluency in their second language as young adults. Centre of mass calculations revealed that these activations were in the region of about 8 mm apart. In direct contrast, those subjects who had acquired two languages simultaneously during an earlier stage of development tended to represent both languages within a single area of activation within Broca’s area. In addition, there were no differences in the activation patterns observed in Wernicke’s area (Brodmann’s area 22) between the subjects who had acquired their second language during early or later stages of development. One interpretation of these results is that the age of language acquisition may determine the functional organization of the language areas within the frontal lobe.

in

RaterA

Review

of

Press

Nature

0 1997, Elsevier Cognitive

K.H.S.

associated

Science

Sciences

et al. (1997) with

native

Distinct and

cortical

second

areas

languages

388. 171-174

Ltd. All rights -

Vol.

reserved. 1,

No.

1364-6613/97/$17.00 5,

August

1997