Learning Impairment (Lli) Speech Perception

¶ … Learning Impairment (LLI)

Speech perception refers to a person's ability to hear and then understand or break down the hearing into comprehensible linguistic parts (Kuhl, 2004). For most people, this process comes naturally. However, to some, speech perception may lead to a language learning impediment. Research in this field yields compelling as wasll as practical results to help individuals suffering from language impairments. In fact, two independent research studies report that language learning impaired (LLI) children improved by approximately two years after only four weeks of intensive exposure to speech and language listening exercises presented with an acoustically modified speech signal, together with a new form of adaptive computer training (Tallal, Miller & Bedi, 1996).

The study under review herein explains the connection between how speech perception deficits themselves lead to language learning impairment (Ziegler & Pech-Georgel, 2005). Since nearly ten percent of students have a language learning impairment which interferes with his or her ability to process language and hence to learn, it is critical that research continues in this area so that early diagnosis and treatment can be applied to help these children process and comprehend speech ("Specific Language Impairment Due to Inability to Process Sound Normally," 1995).

2. Definition and Explanation of Speech Perception

Simply stated in layman's terms, speech perception is the ability to hear and understand speech (Kuhl, 2004). Speech perception technically refers to the process whereby an utterance is decoded into a representation in terms of linguistic units (sequences of phonetic segments which combine to form lexical and grammatical morphemes) ("Speech perception," n.d.).

Research in this area has progressed tremendously in the past fifty years such that we understand that speech perception is a "product of innate preparation (nature)" and "sensitivity to experience (nurture)." Specifically, infant studies have shown that they respond to speech signals in a special way that leads to a strong suggestion of an innate component to language learning. Further research has found a strong environmental influence on the effect of the environment upon language acquisition since we know that the language that an infant hears during the first year of his or her life allows the child to produce a specific set of sounds depending upon the language or languages uttered by the child's parents. We also understand that speech perception proceeds through a series of stages. Throughout these stages, the receiver of the sound extracts acoustic cues, stores them in sensory memory, and then maps them onto linguistic information (Lane, 2008).

3. Definition of Language Learning Impairment

Most of us do not think twice about processing the sounds we hear. The processing of speech just happens. However, many children cannot hear the difference between certain sounds. Perhaps, the child's brain auditory processing isn't fast enough to hear small differences such as / b / and / d / in order to quickly distinguish between the words "bad" and "dad" in oral speech. When this occurs, this is called a language learning impairment (Merzenich, Jenkins, & Johnston et.al., 1996). According to a later study by Tallal and Benasich (2002), language learning impairments (LLI) are one of the most prevalent of all developmental disabilities. Language learning impairments can occur in children for a many reasons. In fact, LLI's have been found to co-occur frequently with other developmental social, emotional and behavioral disorders. Morever, due to LLI's, students afflicted tend to have academic achievement problems as well (Tallal and Benasich, 2002).

4. Brain Substrates of Speech Perception

The past fifty years has seen an explosion with regard to knowledge of how speech and language is associated with specific brain processes. For nearly a century, medical practitioners followed Wernicke's 1874 neuroanatomical model of speech perception which did not take into consideration phonetic cues or even phonemes themselves (Binder, 2000). In the past decade, scientists using functional neuroimaging have repeatedly observed a superior temporal region in both hemispheres of the brain that activates more strongly to speech than to non-speech sounds like tones and noise. The location of the speech center was surprising because the traditional Wernicke model emphasized the significance of the posterior part of the superior temporal gyrus; however, recent findings using modern technology revealed that the speech-specific activation actually lay anterolateral to primary auditory cortex and anterior to the mid-point of the gyrus. In fact, the planum temporale which had for many years been considered the speech center did not show a preference for speech sounds. In sum, new studies revealed that the projections from primary to secondary auditory cortex which enables speech recognition follows an anterolateral rather than a posterior course (Binder, 2000).

5. Experimental Paper: Summary of Hypothesis, Methods, and Results

In the experimental paper "Deficits in speech perception predict language learning impairment" by Johannes C. Ziegler, Catherine Pech-George, Florence George, F.Xavier Alario, and Christian Lorenzie (2005), researchers investigated the acoustic and phonetic nature of potential speech deficits in children with specific learning impairment (hereinafter referred to as SLI). Prior to embarking upon the study, these researchers hoped to demonstrate the relative increase in the power of detecting speech perception deficits in SLI when the focus is shifted from purely nonlinguistic auditory tasks to speech identification of phonetic categories. To do so, the experimental design added more phonemes than had been included in previous studies; and, they utilized two types of noise: temporally fluctuating noise and stationary noise. They conducted two types of experiments testing speech identification by two control groups of school children: (1) a group of same aged students, (2) a group of similarly situated learners in terms of language ability. Each group received the two different kinds of noise input of the phonemes selected. The testing itself was administered to the students on an individual basis, not as a group, wherein the students received the input (48 different utterances) wherein they were asked to respond orally or point to the correct response regarding identification of the stimulus.

After gathering all of the data, the researchers came to a variety of conclusions. First, under optimal listening conditions, children with SL1 had only "subtle speech perception deficits." When there was stationary noise or fluctuating noise, however, the SLI children revealed substantial speech perception deficits. This finding leads to the proposition that students with SLI have serious problems in a classroom environment (or any study environment) with the ability to exclude and filter out meaningless noise. The researchers further noted the importance of conducting research under conditions that not only were optimal but included fluctuating noise. As a result of doing so in this study, they found that speech perception deficits interfere in a specific way with the development of phonological representations. Consequently, this interference might also affect other aspects of grammatical development. A further finding revealed that intact masking release was present in children with SLI regardless of the frequency of the noise. This finding allows researchers to, therefore, conclude that the core deficit in SLI children is not due to poor temporal or spectral resolution. Thus, where do these deficits come from? The research herein shows that SLI children have insufficient processing of the information and that this inefficiency is exacerbated by background noise.

6. Experimental Paper: Speech Recognition and Language Learning Impairment