A Unitary Model Of Pitch Perception - Research Paper Example

A Unitary Model Of Pitch Perception Models for the study of virtual or low pitch perception essentially fall into two camps, the first championing the spectral theories and the second the temporal theories. The differences between the two theories can be narrowed down to the kind of harmonics that these two theories lay stress on in the study of virtual or low pitch perception. In the spectral theories the stress is on the results based on low-numbered harmonics, while in the case of the temporal theories the stress is on the high-numbered harmonics. Meddis and O’Mard 1997, suggest that both these theories can be effectively embraced in a single model, resolving them into a single system. This new model finds its origins in the computational model of pitch perception that employs autocorrelation of the estimated probabilities of firings in sets of auditory nerve fibres. Autocorrelation models provide the benefits of being able to predict listeners performances is several important areas, as well as the ability to simulate several components of the sensitivity of listeners to the phase relationships between adjacent harmonic aspects in tone complexes. In the current study Meddis and O’Mard 1997 fall back on the autocorrelation model of Meddis and Hewitt 1991 to evaluate three important phenomena of the pitch of alternating-phase harmonic complexes, difference in frequency limens of virtual pitch and the impact of mistuning individual harmonics on the pitch of the complete complex. The relevance of such a study lies that these aspects can be used to provide justification for the dual temporal and spectral mechanisms in pitch perception. The study involves the evaluation of the suggested model to meet the required predictions in pitch perception. In this study only minor alterations were done to the model of Meddis and Hewitt 1991. Stimuli employed for the study were about 100 ms with an onset ramp of 2.5 ms. The tone components used were harmonic and set at 60 dB SPL and in the case of any deviation, it was clearly stated. The pre-emphasis filter was in essence a simplified reflection of the pressure gain of the middle ear. A set of sixty linear fourth order gammatone filters were employed to mimic the mechanical frequency selectivity of the cochlea. The output emanating from each filter was passed to an inner hair cell models to provide the effect of mechanical to neural transduction. Founded on the firing probabilities a running autocorrelation model was computed in the case of each channel. Results of earlier studies had provided the basis for the posit that perception that was based on resolved harmonics are well accounted for through the use of spectral theories, while on the other hand the perception based on unresolved harmonics was better accounted for through the use of temporal theories. The model under study demonstrated this effect. Earlier studies had shown that there was increase in the frequency difference limen in the pitch of an eleven component harmonic with regard to the number of the lowest harmonic in the complex and this feature was a function of the resolvability of the constituent harmonics. The Meddis and Mard 1997 model demonstrates capability of evaluating and verifying these findings of earlier studies. Evaluation of the pitch of a complex with mistuned harmonics this four-stage periodicity model of Meddis and Mard 1997 shows that there is the likelihood of the process of hearing out a mistuned component comes along with the weakening of the contribution made by that component to the perception of pitch. The model also demonstrates capability of differentiating sounds based on the pitch as a guide to the process. The dominance of individual harmonics based on the models shows that it emanates from a minimum of four subsidiary principles. The model however may not be capable of representing each of these effects with the desired accuracy. The model demonstrates a capability for a wide range of predictions and the results that have emerged show consistency with the findings of recent studies that the perception of pitch based on resolved harmonics will act in a different manner to that which is based on unresolved harmonics. In addition it is found that though harmonics exert a very strong influence on the perception of pitch their relative phases have little influence on the perception. In contrast to this, though unresolved harmonics have a very small role to play in pitch perception, their relative phases have a very important role to play. These qualitative aspects as demonstrated by the model imply that there is no necessity for two distinct mechanisms for the extraction of pitch. The model however falls short of offering a general theory of pitch, as it does not account for address many issues like pitch variation with sound-pressure level, octave enlargement and interaural differences in pitch. (1). Summary – Yost et al 2005, “Pitch strength of regular-interval click trains with different length ‘‘runs’’ of regular intervals”. Over the last decade there have been several studies into the pitch perception of click trains, wherein manipulations of statistics in different ways have been effected on the intervals between clicks for the study purposes. An aspect that stands out in these investigations is the evaluation of the first-and second-order intervals between clicks. First-order intervals consist of the intervals between successive clicks, while second-order intervals are made up of the intervals between every other click. Evidence from these studies show that there is less sensitivity of the auditory system to second order clicks. Autocorrelation analysis used in evaluating pitch and pitch strength of complex sounds are not sensitive to the order of intervals present in a click train. These findings suggest that autocorrelation may not be a suitable mechanism on which to base the models of the auditory processing of regular interval stimuli. The Yost et al 2005 study attempts to bring out another deficit of the autocorrelation function or long-term spectrum as a model for auditory spectrum, using the statistics of the regular interval click trains. Click trains with a repeating alternation and random intervals that produce a pitch at the reciprocal of the time duration of the fixed interval were generated for the study. The time intervals were then shuffled on a random basis and a comparison done with the un-shuffled alternating click trains in a set of pitch-strength comparison experiments. Results in most of the comparisons of the first-order interval stimuli showed that the randomly shuffled-interval click trains possessed a stronger pitch than in the un-shuffled-interval click trains. In addition the shuffled-interval click trains only generated stronger pitches for second-order interval stimuli in unfiltered click trains. Many of the experimental conditions and an evaluation of the runs of regular and random intervals in the studied click trains raise speculation that auditory system sensitivity is influenced by the presence of a mix of regular and random intervals in the runs of the regular intervals employed as the stimulus. Such implications indicate that fine-structure regularity has a more significant role to play in pitch perception rather than randomness and in addition long term autocorrelation or spectra of such click trains are unsatisfactory predictors of pitch strength. The emerging evidence that runs of regular intervals gave a greater influence on the perception of pitch than runs of random intervals raises the possibility of the auditory system being more susceptible to the regularity than randomness. An additional suggestion that emerges from this study is that since only two or three consecutive regular intervals have an have an influence on pitch-strength judgements, the auditory system is extremely sensitive to the regularity in a complex sound. (2). Summary – Moore, A. L. & Davis, B, 2002 “Quilting Narrative: Using Repetitive Techniques to Help Elderly Communicators”. Personal narratives find a place among the several ways in which individuals share themselves with others. In individuals experiencing cognitive difficulties the ability to weave a story into the give and take pattern of a conversation may be diminished. Health professionals can aid in this process of weaving the story into conversation. However, the ease with which this support can be provided depends on the extent of the knowledge of the components of the narrative. During the process of quilting a narrative, the health professional gets involved with the individual in narrating the story and provides assistance in constructing it. The assistance is in the form of health professional repeating an utterance of the individual that may have been heard as a part of a story or a from the individual, or another care giver’ or a family member and pausing to give the individual the opportunity to add a new part to the story. During a subsequent meeting the health professional introduces the details provided by the individual and again pauses for new additions. In a gradual and continuing process the health professional assists the individual in weaving the story. A lot of effort and practice go towards acquiring the required skills. The repetitive skills needed for this process are used in everyday life, but without noticing it. In normal interaction with friends and colleagues, when a detail is omitted, we repeat the part with the detail and get the full narrative. This is exactly what is done in the process of quilting with individuals with cognitive deficits, the difference being that it is a longer and painstaking process with the requirement for many more reminders. Individuals with cognitive deficits like in Alzheimer’s disease (AD) could become frustrated, when unable to put the full story together. Assisting them in weaving their story reduces their frustration and agitation. Moore and Davis 2002 suggest four basic strategies to help individuals with AD express themselves. These strategies are estimation of the probable expectations of the content of the story and the manner in which it will be narrated and providing alerts when there are deviations; signalling the initiation of the narrative and giving context through some sort of abstract or orientation; monitoring for the need for clarifications and additional details and ensuring that the story remains on track, with an ending that contains evaluation of some elements of the narrative. Using the experiences of successful use of quilting narratives with two individuals in special care units, Moore and Davis 2002 attempt to highlight the different narrative components in these conversations. These results show that in conversations with individuals with AD, there is the need to try and identify anything that sounds like the start of another story; another event; or the repetition of other details. Such repetition implies that there is another story waiting to emerge. It is also useful to try and identify the end of the story or for another event that has some connection to the preceding conversation. A better understanding of narratives as seen in normally aging adults paves the way for an understanding of narratives in adults with cognitive deficits and the deciphering that the deficits in the narratives are not oriented to language loss. This understanding also assists in the selection of better interactive means to provide meaning. For example in individuals with AD, support can be provided by reintroduction of details of earlier conversations that assist recognition and lead to expansion. The use of the repetitive technique of the quilting narrative by health professionals enables the family members to realize that the individual with cognitive deficits is signalling some part of an event or an identity. The use of the quilting narrative to assist in completing the story provides the benefit to the care giver of understanding the individual with a cognitive deficit better and benefits the individual in quilting sections of their life, thereby providing mutual benefits to the care giver and the individual. (3). Works Cited 1. Meddis, Ray & O’Mard, Lowel. “A unitary model of pitch perception”. Journal of the Acoustic Society of America 102.3 (1997): 1811-1820. 2. Yost, A. William, Mapes-Riordan Dan, Shofner William, Dye Raymond & Sheft Stanley. “Pitch strength of regular-interval click trains with different length ‘‘runs’’ of regular intervals”. Journal of the Acoustic Society of America 117.5 (2005): 3054-3068 3. Moore, A. Linda & Davis, Boyd. “Quilting Narrative: Using Repetitive Techniques to Help Elderly Communicators”. Geriatric Nursing, 23.5 (2002): 262-266. Read More