Auditory Perception

AUDITORY PERCEPTION • • • • It is particularly true, for the auditory modality, that the signal, which carries the message, is transient. It lasts for only a brief moment in time and is gone. Hence, the speed and efficiency of the processes that decode the signal are critical. Speech is probably the most difficult of the auditory signals to process. It contains a stream of multitudinous and rapidly modulated variations. Some of these change the meaning a lot, some change it a little, and some have no effect on the meaning. In addition, meanings are being transmitted simultaneously on several levels including: non linguistic, phonetic, morphologic syntactic, semantic and pragmatic. As difficult as it is, we (humans) make it look easy. Figure-Ground discrimination is sometimes referred to as Signal to Noise Discrimination in the Auditory Modality. • • There can be little doubt that we have received a genetic inheritance of basic neural networks that make our amazing auditory perceptual skills at all possible. And then we spend many years building upon and perfecting these networks. Auditory perception involves many processes, and sub processes and sub sub processes, all of which are important. • To discuss them all would require almost taking a major in Psychology. For now we will examine the following select group of major processes: Figureground discrimination; Closure; Temporal Resolving Power, and Memory. 1. Figure (Signal)-Ground (Noise) Discrimination: We have discussed figureground in generic terms, and have provided examples for the visual modality. There are two types of figure-ground task. They are really opposites ends of a continuum. At one end is an Aural figure-ground task and at the other is a Statistical figure ground task. • An Aural figure-ground task is one in which the figure and the ground are unmistakably different. It never fails, when you are in a class and the instructor says "Listen carefully because this will be very important¸" that a loud lawn mower and/or a leaf blower will pass by the window. o To say that it is very difficult to concentrate under such conditions is to have commented on an aural figure-ground task. Or worse yet, someone with a nasal-dripping cold (as demonstrated in the Notes) sits behind you in class with much audible sniffling etc. In an Aural Task, the Signal and the Noise are different, but in a Statistical Task, they are similar. Neither the lawn mower nor the sniffling would be confused with the speech signal, but they create a significant figure-ground task for the brain, which must internally suppress the racket while interpreting the speech. The Statistical figure-ground task is even more challenging. This is a listening situation in which the figure and the ground are very similar. o • o o Any teacher or parent who has tried to listen to two or more kids simultaneously telling about something that happened, will know the difficulty of this task. During the second World War in England there were many instances when planes (many in dire distress) were returning from missions and requesting emergency landing instructions. For children with Figure-ground processing problems, noises prevent them from understanding much of what is said. o o The tower operators had to listen to simultaneous voice transmissions over the same radio band, and make decisions about who was saying what. Some children (and adults too) have particular difficulty in discriminating speech or other sounds in the presence of back ground noises--even small ones. For them noises are more than minor o o o o o annoyances. They are a major cause of learning disabilities. These individuals are constantly switching their attention to unimportant sounds such as foot scraping, light buzzing, whispering, pencils falling, blowing wind and fans etc. etc. etc. Hence, they miss most of what they need know, and find listening unrewarding, if not fatiguing. Conversely, it is possible to improve this perceptual ability with practice. Exercises can be created to target sounds embedded in varying degrees of background noise. These can be both fun and productive in developing these skills. One clever battery of training exercises was developed, for example, by the Alameda County School Department in California. Some excerpts from this and the Goldman-Fristoe-Woodcock Test batter are in the Notes. 2. Auditory Closure. Auditory closure is a process of filling in the missing pieces of the figure. Often the noise, (another word for ground) which accompanies the signal (another word for figure), actually obliterates some of it. Quite often it is the higher frequencies which are lost. For the speech signal, this tends to mask many of the consonant sounds. A person with a high frequency loss experiences this loss all the time. Although closure typically depends upon learning, its application is often automatic and unconscious. But for a person with a high frequency hearing loss, low frequency environmental noises often mask many of the remaining vowel sounds upon which they depend for important cues. Hence their hearing loss seems much worse than would be expected when there is a lot of noise o In all of these instances, to obtain the meaning, the brain must internally reconstruct the signal and fill in the missing parts. o This is one form of auditory closure. Sometimes, the closure is so automatic and efficient that we are hardly aware that some of the consonants are missing. In the notes you will here a list of words with missing consonants. See if you can understand these words or tell which consonants are missing. o • Auditory Blending involves bringing the fragments of a word together to obtain its meaning. o o o It is not only noise, however, that can degrade a signal. Sometimes, the information part of the message (the figure) is dismembered. For example, what is this word: "c________a________t________a________p______ __u________l________t" You probably sounded it out in pieces and then pulled it together in mental closure process. o o o The meaning of the word "was catapulted" into your consciousness, and the experience was relatively rewarding (granted the perks in my life are probably a little more reserved than for most students). This type of auditory closure skill has a special name, "BLENDING", and it plays a major role in reading. If a child has a processing problem in blending, trying to learn to read using the phonics approach can be very frustrating and unrewarding.. Many fun games and activities can be created to exercise Blending and other perceptual skills. o o o o I have found many non readers at the Junior High level who still cannot blend sounds. In some cases it's a persistent perceptual deficit. In others it is a psychological overlay (i.e., history of failure) that discourages them from even trying. While I don't advocate formal reading instruction for preschool and kindergartners, I do encourage fun activities which involve practice in closure tasks. For very young children, Piaget suggested partially hiding objects. He, of course, was talking about teaching object permanence to babies, but the principal is the same. For example, an activity might involve partially hiding three different dolls under pillows and asking the child to find a particular one. Of course, that was the visual modality and we are talking auditory here. Many four year old children love to guess the names of words given to them in peices, like "potat.......to." With my four year old, at first we made two choice games. I would say, "toma.......to;" and then she would guess whether it was "tomato" or "pillow." The success rate was high here, and that is very important. Later we would just practice straight blending, although with syllables and not phonemes. In giving me a hint about a birthday present I was getting, my four year old said they were fuzzy and warm, went on the feet and started with the sounds..."slip...." Because, I was a little slow in the closure, she after about 30 seconds added the ..."er." The notes below have some test & training examples in blending for older children. Auditory Closure is needed to correct the distortions of speech. o o o o Sometimes, the speech signal is neither embedded in a distracting ground nor disassembled. But it may, nevertheless, require closure, because it is distorted. The most common and important examples of this are cases involving a foreign dialect. Many highly talented people come to another country and contribute much to the new community. Even though they may speak the new language, however, communication often remains a serious problem because of their foreign accent. Can you imagine the stress that could be created for a nurse (not to mention the patient) at an operating table if she wasn't sure what instrument the doctor was asking for, because of his accent! In the notes is a similar, if not scientific example. 3.Temporal Resolving Power is the ability to handles rapid sequences of sounds. • Temporal Resolving Power: Most auditory stimuli come in sequences over time. Typically, the succession of events is very rapid. There is, however, a limit to the ability of the perceptual system to discriminate the discreteness of successive stimuli as they come closer together in time. For example, if two clicks occur far enough apart in time, you would definitely hear two clicks... When two successive sounds come too close together, some individuals may hear only one. o If they were even closer in time, you might still hear two clicks, although someone with a brain dysfunction might only hear one. o But, if they were even closer, although there will still be two clicks, we all would eventually come to the point where we would perceive only one. Eventually a threshold is reached where everyone hears just one of two rapidly presented sounds. • • This is interesting (possibly), but does it have any relevance to speech and language, you may ask. Yes most definitely. The ability to hear even the occurrence of some consonants (which occur as sounds in quick succession with vowels) depends on this ability. The principle is the same for distinguishing the order of rapidly presented series of different stimuli. Speech, itself, is nothing but sequences of different stimuli (phonemes), and perceiving their order is more than half of the decoding game. If the phonemes are far enough apart in time, you can perceive their order. Perceiving the order of successive speech sounds depends on their speed of delivery. • Speech, itself, is nothing but sequences of different stimuli (phonemes), and perceiving their order is half of the decoding game. If the phonemes are far enough apart in time, you can perceive their order. • As they get closer together in time you may still perceive their order... ...but for someone with lesser perceptual processing power... Some individuals may not be able to perceive the order if they come too fast. • • ...such as young children with immature neural networks; individuals with brain dysfunction or much older folk like me (with both thinning hair and brain cells) may become confused. Now we don't know whether the order was CAT or TAC or ACT. In speech, of course, it makes a big difference. Understanding the order of sounds is also critical for decoding morphological structure and meaning of words. • As you can imagine, the possible combinations increase wildly. Was the word SCAT, TASC, TACS, CATS, etc. etc.? What a confusing task for someone with weak Temporal Resolving Power! Notice, however, that not only the meaning of the word is at risk, but also the meaning that may come through the structure of the bound morphemes! "Fast Forward" is a computer program that slows down the presentation of consonants. • • If a child doesn't perceive the "s" and other bound morphemes on the ends of words, how will he/she learn the principles of grammar, such as plurals and possessives and such? This can impact negatively upon children's language development, reading skills and academic achievement. The problem of sequencing for some children has been addressed in recent years by a computerized program called "Fast Forward." • This program is produced and marketed by the Scientific Learning Corporation in Berkeley, California. In this program, consonants are prolonged to provide greater time for the child to process and recognize the order of phonemes. The notes below provide respectively, the Company's Web Page, information on Fast Forward, a discussion and a Sample movie. Games and listening oriented activities will improve Temporal Resolving Power. • • • • Of course, providing listening opportunities for very young children would seem highly advisable to nurture the development of the neurological infra structure that will enable good listening skills for the future. This can take the general form of multiple daily readings (initially nursery rhymes which provide rhythm, intonation and rhyming. This should be start very early. I would consider from one week after birth to 14 years, although you can begin to think of broadening the scope from nursery rhymes after two and a half years. Later, training can take a more structured form like listening centers with games and exercises for children. In the notes are some exercises for school age children. The localization of a sound depends also on Temporal Resolving Power. • Sound Localization: Because we may not consciously perceive the order, or even the discreteness of two very close successive stimuli, it does not mean that our perceptual system has lost track of the time intervals involved. • • • • We actually are still processing them, but at a different level and in a different way. Take for example a sound that comes to us from the extreme right side. The sound wave first reaches our right ear, and then must travel the width of our face to reach the left. There is a brief time interval involved between the stimulation of each ear. This is maintained as the sound continues in the form of a difference in phase between the input of each ear. But, the time interval is too brief for us to perceive two sounds. Sound Localization (like stereopsis) requires two normal transducers (ears) . • • • • The brain is still actually receiving two sounds, and processes the time difference between each to produce the illusion of a sound localized in space! As the sound source moves toward our center (front or rear) the time differential between the ears decreases and the sound appears to move towards the center. We are, at any point in time, only aware of the location of the sound in a single horizontal plane to the right or left. If it is a brief sound, we can't really ascertain whether its source is to our front or back, or above or below us. But if the sound persists, we will without realizing it make small adjustments of our head (ears) to sample several different planes and quickly zero in on the sound source. • For the most part it takes two ears to perceive location of the source of a sound. The sound localization process facilitates figure-ground discrimination. • • • • • • There are some sophisticated, if not minimal cues for location that do come from a single ear in the form of the resonance created in the Pinna. This is discussed briefly with some references for anyone who is interested, in the notes below. There is one more contribution of Temporal Resolving Power, which I would like to point out. It is the interaction of sound localization with figureground discrimination. You might have noticed, if you have ever taped a lecture and listened to it later, that you were more aware of all the background noises than you were in the actual classroom. This is because in the classroom, you were able to use sound localization to identify noise sources. A person with only one good ear will learn language normally, but will have to work harder to understand speech in a noisy environment. • • • When you listened to the tape, however, the sound source was all from one direction and figure-ground discrimination becomes a more difficult task. Hence, a person with one good ear may hear sounds as loudly and clearly as anyone else, but will experience more confusion and fatigue in a noisy environment. The same is true for someone with a hearing aid, which has only one microphone to pick up the sound signals. 4. Auditory Memory: • Memory, of course, is a major component of our neurological armament. It is a massive process that is involved in almost all other cognitive skills. Scientists spend their lives studying it, and still we don't know the basic mechanisms involved. But there is much information we do have, and we will look at some of this later. Because the speech signal is discursive and transient, memory must retain it until decoding takes place. • But for now we must acknowledge the role of memory specifically in the auditory process. Two things are critical in audition. The auditory stimulus is transient, and the message is discursive. That means the signal is strung out in time. It doesn't hang around long enough for us to experience the entire message in one "sitting," like we can when we observe a picture. • • • In audition, it remains for the processes of memory to hold on to the pieces of the stimulus that have faded, so that we can deal with them as if we had the whole. Note that I said processes (plural), because memory (like language) is a system of many sub processes. Of the many memory sub processes, we will mention two for now: Short-Term and Long-Term memory. Short-Term Memory, is the ability to hold on to the signal for short periods of time--from milliseconds to hours. It is not, however, a single process but a group of sub sub processes: Sensory, Perceptual and Wrote Memory. Sensory short-term memory, pertains more to the action of the transducer. In many respects it is the counter part of after imagery in the visual but with a different purpose. o Sensory short term memory holds the image from the transducer long enough for us to recognize is structure. o Without the after glow on a radar screen, for example, patterns would be difficult to discern. Sensory short-term memory performs the same purpose. It enables us to recognize sounds patterns, like phonemes. Perceptual short term memory, relates to our ability to retain strings of words while the brain decodes their phonological, morphological, syntactical, semantic and pragmatic significance. This is truly an amazing process! o • • People often talk to us in long complicated sentences. The meaning of any sentence can only be obtained from an analysis of the interrelation of all the words taken as a whole. • • • • • • The sentence must also be analyzed in terms of a sentence that may have occurred earlier in the conversation. There may be 20 to 50 words in a sentence. We must hold on to the words, extract the meaning, and do it fast enough to be ready to receive the next sentence which comes right on it(tm)s heels, and the next and the next. What makes it truly amazing is that typically we are limited to approximately 7 bits of information for this short term memory process. We obviously do more by using various organizational strategies. One important strategies is expectancy. It's interesting that most computers have some of this now in the form of word prediction. You start to type something and the word appears before you finish. Context and and particularly grammar are important features of expectancy which broaden our input capacity. For a child (or adult) with severely limited short term memory (say 4 or less bits in information) and with few strategies to rely on, (e.g., poor grammar and/or a dearth of life experiences) decoding an oral sentence can be a significant problem. A child with a very restricted short-term memory may have difficulty understanding long sentences. • I actually experienced a similar situatiion in Latin II class. I did well with Caesar who came, who saw and who conquered Gaul; and wrote about it in short sentences. • • • But when I enrolled in Latin III (buoyed by my apparent success in Latin II) I was in for a "Custer's Last Stand" experience. Here we read the works of Cicero who never wrote a short sentence, I am sure, under two pages long. I could never get a complete sentence into my all at once head. By the time I got to the verb phrase through all the relative clauses etc., I had totally forgotten what the noun phrase had been, not to mention the information that was in all the subordinate and embedded clauses. My short term memory, I believe, would have to have been 21 bits to get the whole Latin Cicarian sentence. Ceasar was easier to understand than Cicero (at least for me) because the latter used very long sentences • • • • Granted I had a poor sense of the Latin grammar too, which didn't help my short-term memory. But, I think I know now why Rome declined. They couldn't understand each other with these long sentences. Just kidding, Latin scholars. Auditory Perceptual short term memory is often tested in older children by having them repeat a series of numbers of increasing length. An example from the ITPA is provided in the Notes. • Wrote memory is the short term memory process we use to hold on to information long enough retain lists of items to get from the store, or facts to regurgitate on a test. We use Wrote Memory to retain information long enough to be processed into Long-Term memory. o Unlike perceptual short term memory which lasts for fractions of a second, this process can last for hours. o o o o o It is also useful for holding on to information long enough to convert it into long term memory, but that is a later discussion. There is much that we can do with our young children to develop perceptual and wrote memory skills. Reading to the child (the infant too) is a major positive step. Putting TV in the locked closet is another. Suffice it to say that the brain waves of a person watching the typical TV shows are similar to a person who is asleep. I see limited brain growth there--and a whole lot of wasted time where growth could have taken place.. To be honest, I believe there are a few TV shows which do have merit. There are many activities that will improve the short-term memory process. o o o o I have already mentioned "Mr. Rogers' Neighborhood". As being excellent for a number of reasons For this show I would let the child in the closet, with the TV, but not until he's three years old and then for no more than 1/2 an hour a day. I would ban all shows with cartoons. Almost any children's game is beneficial for developing short term memory. Later on chess is outstanding for this purpose. Theater group play acting is another excellent source of short term memory practice. Equally important are activities like learning to recite poems, starting with nursery rhymes and • continuing, much later on, of course, with things like the Declaration of Independence, and world class poetry. o Not only do these activities provide vocabulary and concepts, but they, more importantly I think, facilitate the neural infra structure for short term memory which will serve the child for a life time. The rule of thumb, here, is to involve the child as Long Term Memory: Long term memory is, of course, indispensable in any decoding task. Without it, no meaning can be attributed to the percept.