tasks differentially recruiting the two.Farah(19)distinguishes one unfamiliar to the subject being just as disruptive as words in his or imagery component that is principally concerned with the represen- her native tongue and nonsense syllables being as disruptive as tation of pattern information and that involves the occipital lobes meaningful words.The effect is not due to simple distraction, from a second more spatial component that scems to be dependent becausc loud bursts of noise have little or no effect (25).These on parietal lobe functioning.Neuropsychological evidence supports results are interpreted under the assumption that disruptive spoken this dichotomy,with some patients having great difficulty in imag- material gains obligatory access to the phonological memory store. ing and recalling such visual features as the shape of the ears of a 3)The word-length effect.This provides evidence on the nature of spaniel dog or the color of a pumpkin but having no difficulty in the subvocal rehearsal process.Memory span for words is inversely spatial tasks such as describing routes or locating towns on maps; related to spoken duration of the words.Subjects can generally other patients show exactly the reverse pattern of deficits(20). remember about as many words as they can say in 2 seconds(26). Having found ways of scparately disrupting spatial and verbal This phenomenon accounts for differences in digit span when processing,one can explore the relative contribution of different subjects are tested in different languages;languages in which digits subsystems to complex tasks.One example of this application tend to have long vowel sounds or more than one syllable take concerns the nature of the cognitive processes involved in playing longer to rehearse and lead to shorter memory spans (27).The chess.The literature reviewed by Holding [in(21)]indicates that model can also explain the marked tendency for digit span in both visual and verbal coding have been claimed to be crucial by children to increase with age;as children get older,they are able to different studies that principally rely on subjective report.We have rehearse faster (28). sought more objective evidence through a series of experiments that 4)Articulatory suppression.It is possible to disrupt the use of utilize the secondary-task technique to disrupt either the phonolog- subvocal rehearsal by requiring subjects to utter some repeated ical loop,the sketch pad system,or the central executive.Our first irrelevant sound,such as the word "the."This process,known as study involved memory for complex chess positions and tested articulatory suppression prevents the subjects from rehearsing the subjects ranging from the modest club player to the international material they are trying to remember and thus removes the effect of grand master.As expected,expertise correlated highly with memory word length.Suppression also prevents subjects from registering performance,but all subjects showed the same basic pattern:no visually presented material in the phonological store.Recall of such disruption from the concurrent verbal task but clear impairment visual material is reduced,and the acoustic similarity effect is from the tasks occupying the visuospatial sketch pad or the central abolished (29). executive.A second study required subjects to choose the optimum The performance of neuropsychological patients with impaired next move from a complex middle-game position and found exactly short-term memory can also be explained as a deficit in the phono- the same pattern.Disruption of verbal activity had no effect,whereas logical store.They typically show no evidence of phonological visuospatial disruption was clear,and this problem-solving task was coding in memory tasks when presentation is visual,no word length even more susceptible to central executive disruption than the task in effect,and no influence of articulatory suppression,suggesting that the first study (22). these patients make little or no use of their defective phonological short-term store (30). Analyzing the Phonological Loop The Function of the Phonological Loop The phonological loop is probably the simplest and most exten- sively investigated component of working memory.It lies closest to Patients with a specific phonological loop deficit seem to have the earlier concept of short-term memory and has been investigated remarkably few signs of general cognitive impairment.Although most extensively with the memory-span procedure.It is assumed to they typically have difficulty in comprehending certain types of comprise two components,a phonological store that can hold complex sentences,interpretation of results in this area remains acoustic or speech-based information for 1 to 2 scconds,coupled controversial (31).The most commonly held view is that the with an articulatory control process,somewhat analogous to inner phonological store serves as a backup system for comprehension of speech.This system serves two functions;it can maintain material speech under taxing conditions but may be less important with within the phonological store by subvocal repetition,and it can take simple,clearly presented material. visually presented material such as words or nameable pictures and In recent years we have been exploring another possible function of register them in the phonological store by subvocalization. this systcm,namely,its role in long-term phonological learning,such This simple model is able to give a good account of a rich range as acquiring the vocabulary of one's native,or even a forcign, of laboratory-based findings.These include the following: language.In one study,we asked a patient with a very specific 1)The acoustic similarity effect.This is the observation that the short-term phonological memory deficit to learn eight items of immediate ordered recall of items is poorer when they are similar Russian vocabulary,a language with which the patient was unfamiliar; rather than dissimilar in sound (23).Hence,hearing and repeating we compared the results with the patient's capacity to learn to dissimilar words such as "pit,day,cow,pen,rig,"is easier than a associate arbitrary pairs of words in the patient's native language(32). phonologically similar scquence such as"man,cap,can,map,mad." People tend to learn pairs of familiar words in terms of their meaning, This phenomenon is assumed to occur because the basic code and,as expected,the patient's performance on this task was entirely involved in the store is phonological;similar items have fewer normal.In contrast,the patient failed to learn the Russian words with distinguishing cues than dissimilar items and are therefore more auditory presentation and was severely impaired relative to control susceptible to being forgotten.Similarity of meaning does not have subjects even when presentation was visual.This result suggests that this effect,suggesting that this subsystem docs not reflect semantic short-term phonological storage is important for new long-term coding. phonological learning.Subsequent studies with normal adults have 2)The irrelevant speech effect.This refers to a reduction in recall of shown that factors that influence the phonological loop,such as lists of visually presented items brought about by the presence of articulatory suppression,word length,and phonological similarity, irrelevant spoken material(24).Once again,the semantic character- strongly influcnce foreign vocabulary acquisition yet show no effect on istics of the material are not important,with a language that is learning to associate pairs of familiar words(33). 558 SCIENCE,VOL.255 Reproduced with permission of the copyright owner.Further reproduction prohibited without permission.Reproduced with permission of the copyright owner. Further reproduction prohibited without permission