Perception and neural representation of suprathreshold signals in the presence of complex maskers

Katharina Egger

06.10.2011 - 18.6.2012

wissenschaftliche Diplomarbeit

Die Arbeit ist bis 22.5.2014 gesperrt.

An important aspect for understanding auditory signal processing is the relation between the physiological (i.e., the neural internal) representation of a sound and its corresponding percept. The present study aims to quantify the perceptual attributes of a signal presented in complex maskers which differ in their effectiveness to mask a signal. While the mechanisms and properties of masking in the auditory system have been studied extensively, the perception of only partially masked (i.e., suprathreshold) signals has not drawn much attention.

To obtain a metric that relates physical properties of the stimulus to its internal representation in the brain, the masked threshold of a signal (target) was modified here by introducing different cues that can lead to a release from masking (i.e., a reduced masking effect). Such cues were coherent masker intensity fluctuations across frequency, so-called comodulation, and interaural disparities in the signal. Suprathreshold perception was assessed by varying the signal level relative to the masked threshold. A perceptual measure was found that described the salience of the target signal (i.e., how well the signal can be segregated from its background). While this measure was primarily determined by the signal level above masked threshold, some effects of experimental condition and subject were found. Further, auditory evoked potentials (AEPs) were recorded to investigate the possibility of a electro-physiological correlate to the perceptual measure of the target's salience. Long-latency amplitudes were found to be sensitive to changes in signal level above masked threshold. However, more test subjects are required to further clarify the relation between the AEPs and the perceptual measure of salience.

Overall, the results suggest that the perceptual salience of a signal embedded in a complex masker is strongly dependent on the masking properties of the individual stimuli, such that salience corresponds roughly to the sensation level of the target and not necessarily to the sound pressure level. It was therefore concluded that cues leading to a release from masking contribute to the general perception of signals in suprathreshold hearing.