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The discrimination of interaural level difference sensitivity functions: development of a taxonomic data template for modelling.

Uragun B, Rajan R - BMC Neurosci (2013)

Bottom Line: This was then followed by PCA to reduce data dimensionality without losing the core characteristics of the data.These seven ILD function classes were found to map to the four "known" ideal ILD sensitivity function types, namely: Sigmoidal-EI, Sigmoidal-IE, Peaked, and Insensitive, ILD functions, and variations within these classes.This indicates that these seven templates can be utilized in future modelling studies.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physiology Department, Monash University, Clayton, Victoria 3800, Australia. uragun@hotmail.com.

ABSTRACT

Background: A major cue for the position of a high-frequency sound source in azimuth is the difference in sound pressure levels in the two ears, Interaural Level Differences (ILDs), as a sound is presented from different positions around the head. This study aims to use data classification techniques to build a descriptive model of electro-physiologically determined neuronal sensitivity functions for ILDs. The ILDs were recorded from neurons in the central nucleus of the Inferior Colliculus (ICc), an obligatory midbrain auditory relay nucleus. The majority of ICc neurons (~ 85%) show sensitivity to ILDs but with a variety of different forms that are often difficult to unambiguously separate into different information-bearing types. Thus, this division is often based on laboratory-specific and relatively subjective criteria. Given the subjectivity and non-uniformity of ILD classification methods in use, we examined if objective data classification techniques for this purpose. Our key objectives were to determine if we could find an analytical method (A) to validate the presence of four typical ILD sensitivity functions as is commonly assumed in the field, and (B) whether this method produced classifications that mapped on to the physiologically observed results.

Methods: The three-step data classification procedure forms the basic methodology of this manuscript. In this three-step procedure, several data normalization techniques were first tested to select a suitable normalization technique to our data. This was then followed by PCA to reduce data dimensionality without losing the core characteristics of the data. Finally Cluster Analysis technique was applied to determine the number of clustered data with the aid of the CCC and Inconsistency Coefficient values.

Results: The outcome of a three-step analytical data classification process was the identification of seven distinctive forms of ILD functions. These seven ILD function classes were found to map to the four "known" ideal ILD sensitivity function types, namely: Sigmoidal-EI, Sigmoidal-IE, Peaked, and Insensitive, ILD functions, and variations within these classes. This indicates that these seven templates can be utilized in future modelling studies.

Conclusions: We developed a taxonomy of ILD sensitivity functions using a methodological data classification approach. The number and types of generic ILD function patterns found with this method mapped well on to our electrophysiologically determined ILD sensitivity functions. While a larger data set of the latter functions may bring a more robust outcome, this good mapping is encouraging in providing a principled method for classifying such data sets, and could be well extended to other such neuronal sensitivity functions, such as contrast tuning in vision.

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Related in: MedlinePlus

The Scree-plot used for determining the number of principal components. The Scree-plot (the lines above the bar plots) and variance explained by the percentage bar plots, are both used for the number of principal component selection towards PCA for seven normalization techniques. Raw (A) and seven different normalized data (B-H) all applied for PCA. In a result, the variances information of each set of principal components (PC1, PC2, PC3 … and PC13) is extracted from the PCA to show the significance. Either higher variance values of principal components, or prior to bending point “elbow” in the Scree-plot, they both indicate necessary number of principal component usage for the reduced data dimension representation.
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Figure 3: The Scree-plot used for determining the number of principal components. The Scree-plot (the lines above the bar plots) and variance explained by the percentage bar plots, are both used for the number of principal component selection towards PCA for seven normalization techniques. Raw (A) and seven different normalized data (B-H) all applied for PCA. In a result, the variances information of each set of principal components (PC1, PC2, PC3 … and PC13) is extracted from the PCA to show the significance. Either higher variance values of principal components, or prior to bending point “elbow” in the Scree-plot, they both indicate necessary number of principal component usage for the reduced data dimension representation.

Mentions: The normalization test bench analyses detailed above showed that the UTPM data normalization technique appeared to be the most suitable normalization technique to reduce the variance in our electrophysiological data. Nevertheless in the PCA analyses, we conducted PCA on all seven normalization techniques to determine the number of principal components needed to account for the variance in data normalized with each of these normalization techniques (Figure 3), as this is an issue that is critical for data classification below. The results are summarized in Figure 3 which presents, for each normalization data type the number of significant principal components together with the variance explained by those principal components, as shown by the percentage data and the Scree-plot in the figure.


The discrimination of interaural level difference sensitivity functions: development of a taxonomic data template for modelling.

Uragun B, Rajan R - BMC Neurosci (2013)

The Scree-plot used for determining the number of principal components. The Scree-plot (the lines above the bar plots) and variance explained by the percentage bar plots, are both used for the number of principal component selection towards PCA for seven normalization techniques. Raw (A) and seven different normalized data (B-H) all applied for PCA. In a result, the variances information of each set of principal components (PC1, PC2, PC3 … and PC13) is extracted from the PCA to show the significance. Either higher variance values of principal components, or prior to bending point “elbow” in the Scree-plot, they both indicate necessary number of principal component usage for the reduced data dimension representation.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4126173&req=5

Figure 3: The Scree-plot used for determining the number of principal components. The Scree-plot (the lines above the bar plots) and variance explained by the percentage bar plots, are both used for the number of principal component selection towards PCA for seven normalization techniques. Raw (A) and seven different normalized data (B-H) all applied for PCA. In a result, the variances information of each set of principal components (PC1, PC2, PC3 … and PC13) is extracted from the PCA to show the significance. Either higher variance values of principal components, or prior to bending point “elbow” in the Scree-plot, they both indicate necessary number of principal component usage for the reduced data dimension representation.
Mentions: The normalization test bench analyses detailed above showed that the UTPM data normalization technique appeared to be the most suitable normalization technique to reduce the variance in our electrophysiological data. Nevertheless in the PCA analyses, we conducted PCA on all seven normalization techniques to determine the number of principal components needed to account for the variance in data normalized with each of these normalization techniques (Figure 3), as this is an issue that is critical for data classification below. The results are summarized in Figure 3 which presents, for each normalization data type the number of significant principal components together with the variance explained by those principal components, as shown by the percentage data and the Scree-plot in the figure.

Bottom Line: This was then followed by PCA to reduce data dimensionality without losing the core characteristics of the data.These seven ILD function classes were found to map to the four "known" ideal ILD sensitivity function types, namely: Sigmoidal-EI, Sigmoidal-IE, Peaked, and Insensitive, ILD functions, and variations within these classes.This indicates that these seven templates can be utilized in future modelling studies.

View Article: PubMed Central - HTML - PubMed

Affiliation: Physiology Department, Monash University, Clayton, Victoria 3800, Australia. uragun@hotmail.com.

ABSTRACT

Background: A major cue for the position of a high-frequency sound source in azimuth is the difference in sound pressure levels in the two ears, Interaural Level Differences (ILDs), as a sound is presented from different positions around the head. This study aims to use data classification techniques to build a descriptive model of electro-physiologically determined neuronal sensitivity functions for ILDs. The ILDs were recorded from neurons in the central nucleus of the Inferior Colliculus (ICc), an obligatory midbrain auditory relay nucleus. The majority of ICc neurons (~ 85%) show sensitivity to ILDs but with a variety of different forms that are often difficult to unambiguously separate into different information-bearing types. Thus, this division is often based on laboratory-specific and relatively subjective criteria. Given the subjectivity and non-uniformity of ILD classification methods in use, we examined if objective data classification techniques for this purpose. Our key objectives were to determine if we could find an analytical method (A) to validate the presence of four typical ILD sensitivity functions as is commonly assumed in the field, and (B) whether this method produced classifications that mapped on to the physiologically observed results.

Methods: The three-step data classification procedure forms the basic methodology of this manuscript. In this three-step procedure, several data normalization techniques were first tested to select a suitable normalization technique to our data. This was then followed by PCA to reduce data dimensionality without losing the core characteristics of the data. Finally Cluster Analysis technique was applied to determine the number of clustered data with the aid of the CCC and Inconsistency Coefficient values.

Results: The outcome of a three-step analytical data classification process was the identification of seven distinctive forms of ILD functions. These seven ILD function classes were found to map to the four "known" ideal ILD sensitivity function types, namely: Sigmoidal-EI, Sigmoidal-IE, Peaked, and Insensitive, ILD functions, and variations within these classes. This indicates that these seven templates can be utilized in future modelling studies.

Conclusions: We developed a taxonomy of ILD sensitivity functions using a methodological data classification approach. The number and types of generic ILD function patterns found with this method mapped well on to our electrophysiologically determined ILD sensitivity functions. While a larger data set of the latter functions may bring a more robust outcome, this good mapping is encouraging in providing a principled method for classifying such data sets, and could be well extended to other such neuronal sensitivity functions, such as contrast tuning in vision.

Show MeSH
Related in: MedlinePlus