Wednesday, September 5, 2007

Memory and Language Perception

By Sudipa Sarkar
Working Memory

Working Memory (WM) is a very newly adopted phenomenon of short-term memory (STM), a significant theoretical framework within cognitive psychology. This refers to the structural outlines and procedures used for momentarily storing and manipulating of data. In 1974, Baddeley and Hitch proposed multi-component model of working memory, in which they have described that two ‘slave systems’ are accountable for short-term maintenance of information, one contributes for verbal and acoustic information – the phonological loop and the another one contributes to visual equivalent – the visuospatial sketchpad, and both are reliant on a third attentively-restricted control system – the central executive, ensuring the possibility of conducting more than one task at a given time by virtue of coordination of cognitive processes through the suppression of irrelevant information as well as improper actions. In 2000, Baddeley added a new component to the existing model, known as the episodic buffer, representing the integration of phonological, visual and spatial information in addition to semantic information, musical information, particularly not covered by the traditional ‘slave systems’.
Phonological Loop
The simplest understandable form of the multi-component model of working memory, in which a temporary storage system for acoustic or speech-based information is assumed to be present in order to hold these information arranged in a array of spontaneous fading with a duration of 2 to 3 seconds as refreshed by the process of rehearsal. The process of rehearsal is assumed to entail some type of sub-vocal articulation, not only works for maintaining information within the storage system, but also serves the purpose of registering visual stimuli within the storage, given the objects can be named. Hence, if a small sufficient quantity of information is to be provided, it can be maintained for an indefinite period through the method of continuous rehearsal. The subjects, if conducted a study for assessing the mechanism of phonological loop, will be found to recall a series of letters such B, W, Y, K, R, X, while they will be found to experience difficulty in recalling phonologically similar series of letters such as B, C, D, G, P (Conrad & Hull, 1964) due their less phonological distinctive characteristics which, in turn, make them more error prone and vulnerable to forgetting. Evidence for sub-vocal rehearsal system is prevalent by the word length effect as well, whereby a series of long words such as tuberculosis, university, auditorium, paramedical, opportunity is significantly harder to remember than a series of five monosyllabic words (Baddeley, Thomson, & Buchanan, 1975). The process of rehearsal and production of response are supposed to function in real time, longer words take longer time to coherent, providing more time for the memory trace to fade.
The effect of word length is profound; however, its construal remains somewhat controversial. Quite evidently, longer words take longer time to recall, leading to more forgetting (Cowan et al., 1992). Evidently, a word length effect takes place when output delay is held invariable, either by the use of a probe practice (Henry, 1991), or by recognition (Baddeley, Chincotta, Stafford & Turk, 2002), signifies that the outcome functions at both the on-going level of rehearsal and through the process of forgetting during responding.
Visuo-spatial Sketchpad

This component contributes to the functioning of integrating spatial, visual and to some possible extent kinaesthetic information into a cohesive representation that may be momentarily stored and manipulated accordingly. This component is aligned parallel to the understanding of phonological loop, however, harder to analyse under empirical investigation, due to its greater complexity at least quite a significant extent. It seems that visual and spatial are considered separate but strong interrelated components of the system (Farah, 1988). Various research studies suggest that storage primarily occurs spatially depending on the memory task (Baddeley & Lieberman, 1980), principally visual as corresponding to by colour as well as shape (Logie, 1986) or to some possible extent by motor or kinaesthetic (Smyth & Pendleton, 1990). These findings are aligned with both lesion and neuroimaging studies indicating the system principally, but not exclusively, reliant on the right hemisphere of the brain (Della Sala & Logie, 2002; Smith & Jonides, 1997).
The Central Executive

This component is assumed to be responsible for the attentive management of working memory. It depends significantly, but not exclusively, on the frontal lobes (Stuss & Knight, 2002) and can almost in particular be segmented into a number of executive sub-processes (Baddeley, 2002; Shallice, 2002). Executive processes are considered to be the major aspects contributing to the individual differences within the span of working memory (Daneman & Carpenter, 1980). Working memory span has proved to be a profound interpreter of a wide array of complex cognitive abilities.
The Episodic Buffer

The concept of the episodic buffer primarily stemmed from the idea challenged by the identification of a range of phenomenon not corresponding with Baddeley and Logie model (1999), typically demonstrating two discrepancies within the model. The first discrepancy depicts the allocation of visual and verbal codes in combination with multidimensional representations in long term memory. The second discrepancy illustrates the need for the momentary storage of material in quantities surpassing the ability of either the verbal or visuo-spatial peripheral subsystems. These construes are highly challenged by a significant number of amnesic patients suffering from a gross impairment of long term memory, yet could carry out at a normal level on instantaneous recall of a prose passage consisting of 20 or more conceptual objects, thus significantly beyond verbal or spatial span (Baddeley & Wilson, 2002).
Language Perception
Language acquisition is considered as one of central topic in the field of cognitive science. Language is the primary tool by which one is able to understand other’s thoughts; hence these two factors are intimately related with each other. In the framework of cognitive science, language acquisition is not only an interesting phenomenon, but crucially important issue to be considered that sheds light on several important questions permeate to cognitive science –
• Modularity: whether children learn language by using a ‘mental organ’ which is partially not shared with other cognitive systems such as perception, motor control and reasoning (Chomsky, 1975, 1991; Fodor, 1983)? Or language acquisition can be considered as another developmental problem needs to be resolved by intelligence in order to communicate with other individuals over the auditory channel (Putnam, 1971; Bates, 1989)?
Human Uniqueness: whether humans are the only animals who know to fabricate the language or human children are ‘taught’ language themselves?

Language and Thought: should language be considered as a communicable label onto thought process (Fodor, 1975; Piaget, 1926) or learning a language implies learning to think in that particular language (Whorf, 1956)?
Neuropsychological Explanation of Language Acquisition
During early years of a child’s developmental phase, the maturation of language circuits acts as a driving force underlying the course of language acquisition (Pinker, 1994; Bates, Thal & Janowsky, 1992; Locke, 1992; Huttenlocher, 1990). Prior to birth, all neurons are formed, and they are allocated into their appropriate positions in the brain. The brain size, weight, and thickness of the cerebral cortex (grey matter) get increased quickly in the year after birth. The white matter is particularly responsible for developing long distance connections which are not completed till nine months of age; however, the continuity of the growth persists with the development of myelin insulation throughout childhood. During 9 months to 2 years of age, the synapses keep on increasing to its peak level depending on the brain region available; having about 50% more synapse than the adult. The metabolic activity in the brain region also takes its optimum shape and reaches to the adult level by 9-10 months of age and soon surpasses it, approaches at its peak at the age of four. Synapses shrink from 2 years of age throughout the rest of childhood and adolescence phase, while the brain’s metabolic rate declines to adult levels. It is assumed that the initial linguistic goals like babbling, first words and basic grammar need a minimum level of brain size, white matter, or extra synapses, in the language centres of the brain in particular. This corresponds with the notion that the ability of learning a language declines throughout the life span. The language learning circuitry is assumed to be more synthetic during childhood as the children can learn or recuperate language even when the left hemispheres gets damaged or surgically eliminated in comparison with an adult leading to possibly permanent aphasia (Curtiss, 1989; Lenneberg, 1967). However, researchers have come into conclusion through a major investigation that Wernicke’s aphasics consist of normal lexical access functionalities and that of Broca’s do not. The data in support of this argument is derived from the generalization of studies focusing on lexical priming (Blumstein, Milberg & Shrier, 1982; Katz, 1986; Milberg & Blumstein, 1981; Milberg, Blumstein & Dworetsky, 1987). Hence, Wernicke’s patients show the normal prototype of faster word recognition in semantically facilitating contexts or priming, but this is not the case with Broca’s patients. Moreover, Broca’s priming appears to be provisionally delayed, or more specifically, lexical contact and activation, as derived from priming, looks as if slower than normal fashion (Prather, et al., 1991).
While explaining the language acquisition processes on terms of cognitive theory, the studies conclude that changes in information processing abilities have an effect on language development. Children are found to be selective and they usually pick up information at the termination point of the words (Slobin, 1973) as well as at the initial point and ending point of a given sentence (Newport, et al., 1977), most likely this is due to the fact that these information can best be retained in short term memory. In addition to that, the gradual enlargement of bottleneck for early word allocation apparently sheds light in the general increase in motor planning ability. The language development pattern of a child not yet being mastered with critical semantic difference gets affected by conceptual development as well.

The neurological basis of language perception is always a topic of interests to the modern researchers as it was 100 years before. Recent studies suggest that linguistic inquest in association with neuroscience most readily congregate at the sentence level, which implies that at this level the relations between language organization, processing sources and brain architecture are mainly perceptible.
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