Physiological and Psychological Aspects of Phonemic Perception - Term Paper Example

Phoneme Perception Introduction Introduction Speech perception involves influences of linguistic knowledge and a complex linkage of auditory features onto phonemes. The process of phoneme perception includes both physiological and psychological aspects of perceptual functioning. Essentially, phonemes can be defined as the basic set from which words are built for a particular language. According to Raphael et al (2006), a phoneme is a physical reality which can be taken as the minimum unit of distinctive sound feature. Hence, a person typically responds to the familiar phoneme features that are in a particular sound wave. On the other hand, phonemes can also be thought of mental representations of a psychological equivalent of an empirical sound (Samuel, 2011). Both the psychological and physiological aspects of phoneme perception are vital in the overall understanding of the concept of speech perception. Phonemic Perception The process of speech perception can be analyzed by evaluating the speech sounds that are produced and the way in which they are assigned meaning. Each acoustic signal comprises of a consonant-vowel combination. Basically, vowels are produced by the vibration of vocal cords and consonants are produced by the constriction of the vocal cord. For speech perception to occur, it is imperative that the acoustic signal has to be divided into small but meaningful chunks (Raphel et al, 2006). The phoneme is the smallest unit of a speech that would alter the meaning of a word if changed. Although it is clear that phonemes create syllables which in turn create words, the perception of phonemes is not straightforward. Sound signals for various phonemes overlap one another and can greatly vary due to factors such age, accent and gender. The variable relationship between phonemes and the acoustic sound present a challenge in understanding speech perception. This variability may occur due to differences in the context of the speech. The particular sound of a phoneme in a particular instance is influenced by the phonemes that precede and follow it. The alteration of the sound of a phoneme based on what comes before and after it is known as co-articulation. For example, it has been pointed out that the acoustic details of /b/ in the words bat, boy, but and bird are different (McQueen, 2010). The sound of the phoneme is perceived to be the same even though the sound of the acoustic signal is changed. This implies a form of perpetual constancy in the perception of speech. It is possible to recognize a phoneme even when it appears in different contexts that alter its acoustic signal. It is evident that different talkers speak in different dialects and idiolects. Imperatively, the same word can be spoken in a variety of ways depending on the speaker. For instance, some people may speak rapidly and others slow; some may be high pitched and others low pitched. The outcome of these variations in speakers is that a phoneme can have different acoustic signals. The sloppiness of pronunciation of a speaker can also influence the sound of a phoneme. An individual can pronounce the same phoneme in different ways depending on the mood, nature of relationship to the listener or the occasion. For example, a person can say ‘How are you doing’ in very many different ways. In conversational speech, people do not usually articulate each word completely and this has an implication on perception of speech (Samuel, 2011). Due to the variability in the acoustic signal, the listener has to somehow find a way to comprehend what the speaker is saying. The listeners have to show a level of phonetic constancy in order to perceive speech. Due to phonetic constancy, the listener hears the same speech notwithstanding the variation in sound, who is talking, the speed of talking among other factors. The ability of a person to understand speech under various diverse conditions implies that there are some invariant properties of sound that uniquely identify the phonemes in a speech. The unique identifiers in a speech enable a person to transform information in a variable acoustic signal into meaningful words. Categorical Perception One of the ways in which the speech perception system can deal with the variability of acoustic signals and phonemes is by simplification of what one hears through categorical perception. The concept of categorical perception proposes that a wide range of acoustic signals results in the perception of a smaller number of categories of sounds. In fact, categorical perception is a form of perpetual constancy whereby the listener is tuned to a limited phoneme spectrum. According to the results of experiments conducted to investigate this phenomenon, it was found out that listeners cannot tell differentiate physically different sounds unless they have labels (Moore et al, 2008). For instance, a series of sounds can be made by gradually lengthening the voice onset time for the words ‘dada’ and ‘tata’. Ordinarily, voice onset time for the consonant sound /d/ in /da/ is shorter compared to that of /t/ in /ta/. When these syllables are presented to listeners, all the shorter voice onset time consonants were labeled “d” and the long voice onset consonants were labeled “t”. Listeners have a phonetic boundary within which they can accurately discriminate between the sounds. However, listeners cannot tell the difference between the sounds when they cross the boundary. In this case, all the stimuli on the same side of the phonetic boundary are perceived to be in the same category. When the voice onset time is small, both /da/ and /ta/ were taken to be /da/ and the converse is also true (Moore e t al, 2008). It is therefore evident that the element of perpetual constancy helps listeners to simplify the process of speech perception by having two categories on the phonetic boundary. If the categorical perception was absent, it would mean that listeners had to perceive different sounds every time that the voice onset time changes. It would be practically difficult to perceive all range of the sounds that are present in the environment. Thus, categorical perception helps to make speech perception easier. Multi Modal Speech Perception The perception of speech can be influenced by information from multiple senses. Visual information can compliment the information that is heard in order to enable speech perception. The information that is provided by the face of the speaker can influence how a person perceives a given speech. In some instances, the visual information form the face can even override the actual auditory information that is heard. This concept of integrating sound from multiple senses is known as the McGurk Effect. McGurk conducted an experiment where a listener heard the sound/ba-ba/. A visual stimulation showing a person making lip movements for the sound/ga-ga/ was then added as the sound /ba-ba/ was played. The result was that the listener begun to hear the sound/da-da/. The perception of the listener shifted although the sound played remained the same. This indicates that visual information plays a major role in the perception of speech on top of the auditory information (Samuel, 2011). The audiovisual speech perception phenomenon also applied frequently by people who use information from lip movements to comprehend what other people are saying. In noisy environments, a person may rely on lip the movements of the speaker so as to decipher some portions of the speech that are not audible. According to Moore et al (2008), the ability of a listener to deal with the variability of phonemes is aided by the link between the perception of faces and the perception of speech. The linkage of audio and visual components in speech perception is vital in helping a person to comprehend speech as the two components complement each other. Information from Language Knowledge The knowledge of a language also plays an important role in influencing how speech is perceived by listeners. People use the language knowledge repository that they possess to comprehend the given speech. For example, listeners can still comprehend a given speech even if a phoneme is missing. The concept of phoneme restoration indicates that listeners can reconstruct a speech and fill in any portions that may be missing. If a sound is played with a missing phoneme, a listener can fill in the phoneme by comprehending the meaning of the words of the in the speech. According to Samuel (2011), if a phoneme is replaced in a speech by a cough, some listeners report hearing the phoneme if they understood the context of the speech. Phoneme restoration indicates that speech perception can be determined by both the nature of and the context of the acoustic signal. The nature of the acoustic signal is also known as bottom up processing. Phonetic restoration is more likely to occur in instances where the masking sound and the masked phoneme are similar. If the masked sound is /s/, then a hissing masking sound increases the likelihood of the phoneme being restored by the listener (Raphael, 2006). The listener is influenced by the sound of the mask and easily relates it to the current speech. Longer words increase the probability of phonemic restoration as compared to shorter words. This indicates that top down processing is applicable in aiding speech perception. Listeners use the context that is provided by the longer word to restore the missing phonemes. The concept of top down restoration is a practical application of the law of good continuation although it is only based on knowledge of meaning and language structure (Moore et al, 2008). The restoration effect is strong with real words and it is nearly non-existent for non-words. This implies that the listener draws on the acquired language knowledge to fill in missing phonemes therefore a person cannot fill in what is unknown. Fuzzy Logic Model of Perception (FLMP) The Fuzzy Logic Model of Perception is can also be used to explain the process of speech perception. The process of perceptual recognition involves includes evaluation, integration and decision (McQueen et al, 2010). The exaction of the three processes depends on the stored prototypes that exist in the long term memory. In the evaluation stage, the information in the speech is transformed into psychological values. These psychological values are then integrated to give credence to the various alternative perceptions of the speech. Finally, the decision for the perceptual identification and interpretation of the speech is made depending on the relative degree of support. This theory of speech perception assumes that the source of the speech gives various alternatives and that the alternatives are evaluated independently. It is imperative to note that people’s perception of phenomenon is influenced by several sources of information and therefore a certain level of analysis has to be undertaken before any interpretation is made. The Fuzzy Logical Model of Perception offers a universal principle of perceptual functioning that can be applicable to speech perception. This model of perception takes into consideration the influence of knowledge on human pattern recognition. It should be noted that the Fuzzy Logical Model of Perception offers consistent results when correlated with both the bottom up processing and top down processing. Physiological Aspects of Phoneme Perception The process of recognizing the spoken word and speech perception inevitably involves the brain. The brain forms the physiological foundations through which perceptual functioning occurs. Research indicates that patients with brain damage have language problems that are unique depending on the specific area of the brain that is damaged. Patients with damage to Broca’s area in the frontal lobe are capable of comprehending speech but can only speak in short sentences. On the other hand, patients with damage on the Wernicke’s area in temporal lobe have difficulty in comprehending speech by other people (Moore et al, 2008). Scientific research has also indicated that there are specific areas in the brain that are voice sensitive. Brain imaging studies point out that there is a voice area in the superior temporal sulcul that is mainly activated by human voice. It is imperative that the speech perception process can be analyzed by the use of a dual stream model. The dual stream model proposes that speech recognition occurs in the temporal lobe while the parietal lobe is responsible for the production of speech (McQueen & Cutler, 2010). The perception of speech involves many aspects and it is therefore distributed across many areas of the brain. In this regard, it can be argued that visual information has some level of influence on speech perception. The influence of visual information on speech recognition can either be complementary or correlation. In the complementary mode, vision can provide more information that hearing. For example, the acoustic distinction between some phonemes can be somewhat blurry. The differentiation between “ba” and “ga” can be very subtle and likely to be lost in background sound (Moore et al, 2008). However, the visual representation of these two sounds is very distinct. In this case, the visual aspect compliments the hearing aspect of speech recognition. In the correlation mode, the visual component provides a portion of information that is important in contextualizing auditory information. The two modes through which visual information influences speech perception indicate that the brain uses various areas to process speech. The visual context of the speech is handled by the inferior occipito-temporal region of the cortex. This region specifies the image details comprehensively and offers a link to the auditory information that is heard from the speech. The other stream of speech recognition involves sequential segment analysis. The syllables, words and phonemes of the speech are evaluated dynamically while correlating both the visual and acoustic aspects. Therefore, it is evident that speech perception involves many interconnected areas of the cortex. This can be further elaborated by the consideration of the effect of cognitive factors on speech recognition. According to Moore et al (2008), the context of a speech can have an impact on its overall perception. The familiarity with the speaker’s voice has an emotional effect on the listener which effectively plays a role in his or her perception. It is easier for a person to understand what a familiar voice is saying than it is for a complete stranger. Familiar voices make simplify the speech perception process as the brain already has some background information through which it can map the new input. The concept of experience-dependent plasticity is also a clear pointer to the existence of physiological basis of speech perception. This phenomenon occurs when the brain’s ability to respond to certain stimuli is influenced by previous experiences. The experience-dependent plasticity in regards to functional perception can be deduced by analyzing how the sounds that children are exposed to influence them later in life. Infants can tell the difference between virtually all sounds that create speech sounds in all world languages. However, they lose the ability to differentiate among some of the sounds by the time they reach the age of one. Experiments conducted on American infants of seven months and later on at eleven months indicated that their physiological responses to a pair of sounds changed over time (Raphael, 2006). At an early age, recorded data from electrical potentials from the surface of the cortex indicated that the infants could differentiate between the two sounds. However, at the later age the infants had the same response to the two sounds. This points out that without experience a child loses the ability to discriminate between sounds. The brain is tailored to store the experiences of the language that the child is learning and the physiological response to other sounds becomes the same. The ability of a person to perceive speech is influenced by the previous language experiences of that person. For example, an adult who has only learnt English may find it difficult to comprehend speeches in other languages. In fact, research has shown that it is easier for children to learn new languages than it is for adults. This can be attributed to the fact that the brain of the children has not been comprehensively tied to specific language experiences (Samuel, 2011)). Summary The phoneme is a minimum unit of distinctive sound feature. Thus, the perception of phonemes is an important element in the overall perception of speech. The variability of acoustic signals and phonemes makes perception of speech to be complex. However, the speech perception system uses various methodologies to simplify the process of understanding a speech. One of the psychological elements of speech perception is the concept of categorical perception. People group various phonemes together and this makes it easier to perceive speech even under different contexts. Also, the language knowledge of the listener can aid the perception of speech. This can be attained by phonetic restoration in instances where some phonemes are missing. Human recognition involves the integration of various senses. Hence, people can comprehend speech by using both auditory and visual components. The brain also plays an important role speech perception by influencing how the various phonemes are recognized and interpreted. Current research in the area of speech perception has embraced the concept of integrating bottom up sensory information and top down linguistic information. It is imperative to note that although the relationship between acoustic signal and percept has been established, researchers have not identified all the invariant cues that aid speech perception. However, it is evident that phonemes play an important role in speech perception and further research should be undertaken to explore the cues that can improve dynamic speech perception. References Goldstein, E.B. (2010).Sensation and perception. Boston: Cengage Learning McQueen, J. M., & Cutler, A. (2010). Cognitive processes in speech perception. The Handbook of Phonetic Sciences, Second Edition, 489-520. Wiley Online Library Moore, B. C., Tyler, L. K., & Marslen-Wilson, W. (2008). Introduction. The perception of speech: from sound to meaning. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1493), 917-921. Raphael, L. J., Borden, G. J., & Harris, K. S. (2006). Speech science primer: Physiology, acoustics, and perception of speech. Lippincott Williams & Wilkins. Samuel, A. G. (2011). Speech Perception. Annual review of psychology, 62, 49-72. Read More