This thesis presents data which support cochlear involvement in attentional listening. It has been previously proposed that the descending auditory pathways, in particular the medial olivocochlear system, play a role in reducing the cochlea's response to noise in a process known as antimasking. This hypothesis was investigated in human subjects for its potential impact on the detection of signals in noise following auditory cues. Three experimental chapters (Chapters 3, 4 and 5) are described in this thesis. Experiments in the first chapter measured the effect of acoustic cues on the detection of subsequent tones of equal or different frequency. Results show that changes in the ability to detect signals following auditory cues are the result of both enhanced detection for tones at the cued frequency, and suppressed detection for tones at non-cue frequencies. Both effects were measured to be in the order of ~3 dB. This thesis has argued that the enhancement of a cued tone is the implicit result of an auditory cue, while suppression of a probe tone results from the expectation of a specific frequency based on accumulated experience of a listening task. The properties of enhancement support the antimasking hypothesis, however, the physiological mechanism for suppression is uncertain. In the second experimental chapter, auditory cues were replaced with visual cues (representing musical notes) whose pitch corresponded to the target frequency, and were presented to musician subjects who possessed absolute or relative pitch. Results from these experiments showed that a visual cue produces the same magnitude of enhancement as that produced by an acoustic cue. This finding demonstrates a cognitive influence on the detection of tones in noise, and implicates the role of higher centres such as those involved in template-matching or top-down control of the efferent pathways. The final experimental chapter repeated several of the experiments from the first chapter on subjects with various forms of hearing loss. The results indicate that subjects with an outer hair cell deficit (concomitant with a sensorineural hearing loss) do not exhibit an enhancement of cued frequencies or a suppression of unexpected frequencies to the same extent as the normal-hearing subjects. In addition, one subject with a long-standing conductive hearing loss (with normal cochlear function) produced an enhancement equivalent to that of the normalhearing subjects. These findings also support the role of the medial olivocochlear system and the outer hair cells in antimasking. It is the conclusion of this thesis that enhancement most likely results from a combination of changes in receptive field characteristics, at various levels of the auditory system. The medial olivocochlear system is likely to be involved in unmasking a portion of the signal at the cochlear level, which may be influenced by both acoustic reflex pathways or higher centres of the brain.

This study delves into the syntactic notion of subject relation in Shona with the aim of characterizing and defining it. This is done through analysing data collected from two of the Shona speaking provinces in Zimbabwe, namely, Harare and Masvingo. The data collection procedures involved the tape recording of oral interviews as well as doing selective listening to different speeches. The data were then analysed using the projection principle, noun phrase movement transformational rule as well as the selectional principles established for the subject relation in the other well researched natural languages. The research found out that there is no one single rule that can be used to determine the subject of every possible Shona sentence. One has to make use of all the seven selectional principles established in the well-researched natural languages. The research managed to assess the applicability of the selectional rules in different sentences. The rules were then ranked according to their reliability in determining the subjects of each of the various Shona sentences. It also came to light that the Shona subject relation has a number of sub-categories as a result of the various selectional rules involved in determining them. These were also ranked in a hierarchy of importance as they apply in the language. For instance, whilst some are assigned to their host words at the deep structure or underlying level of syntax, some are assigned at the surface structure level and can be shifted easily. It also emerged that the freedom of the subject relation in the language varies with the sub-category of the relation. It came to light as well that in Shona both noun phrases (NPs) and non-NPs are assigned the subject role. / African Languages / D. Litt. et Phil. (African Languages)

This study delves into the syntactic notion of subject relation in Shona with the aim of characterizing and defining it. This is done through analysing data collected from two of the Shona speaking provinces in Zimbabwe, namely, Harare and Masvingo. The data collection procedures involved the tape recording of oral interviews as well as doing selective listening to different speeches. The data were then analysed using the projection principle, noun phrase movement transformational rule as well as the selectional principles established for the subject relation in the other well researched natural languages. The research found out that there is no one single rule that can be used to determine the subject of every possible Shona sentence. One has to make use of all the seven selectional principles established in the well-researched natural languages. The research managed to assess the applicability of the selectional rules in different sentences. The rules were then ranked according to their reliability in determining the subjects of each of the various Shona sentences. It also came to light that the Shona subject relation has a number of sub-categories as a result of the various selectional rules involved in determining them. These were also ranked in a hierarchy of importance as they apply in the language. For instance, whilst some are assigned to their host words at the deep structure or underlying level of syntax, some are assigned at the surface structure level and can be shifted easily. It also emerged that the freedom of the subject relation in the language varies with the sub-category of the relation. It came to light as well that in Shona both noun phrases (NPs) and non-NPs are assigned the subject role. / African Languages / D. Litt. et Phil. (African Languages)