Speaker authentication and identification were examined for two different methods of presentation of the speech material: (1) speech samples presented aurally through headphones, and (2) speech samples presented visually as conventional intensity-frequency-time patterns, or spectrograms. Two kinds of experiments were carried out: (1) a series of closed tests in which there was a library of samples from eight speakers, and test utterances were known to be produced by one of the speakers; and (2)
a series of open tests in which the same library of eight speakers was used, but test utterances may or may not have been produced by one of the speakers. The results for the closed tests indicate that, after about 4 h of exposure to the test situation, the percent error in identification of speakers from isolated speech samples (words or phrases) is about six percent for aural presentation and about 21% for visual presentation. These scores depend upon the talker, the subject, and the phonetic content and duration of the speech material. For the open visual tests, appreciable numbers of false acceptances (incorrect authentications) were made. The results suggest procedures that might be used to minimize error scores in practical situations.
Activity-dependent changes in hippocampal energy consumption have largely been determined using microdialysis. However, real-time recordings of brain energy consumption can be more accurately achieved using amperometric sensors, allowing for sensitive real-time monitoring of concentration changes. Here, we test the theory that systemic pre-treatment with glucose in rats prevents activity-dependent decreases in hippocampal glucose levels and thus enhances their performance in a spontaneous alternation task. Male Sprague Dawley rats were implanted into the hippocampus with either: 1) microdialysis probe; or 2) an oxygen sensor and glucose biosensor co-implanted together. Animals were pre-treated with either saline or glucose (250mg/kg) 30min prior to performing a single 20-min spontaneous alternation task in a +-maze. There were no significant differences found between either treatment group in terms of spontaneous alternation performance. Additionally, there was a significant difference found between treatment groups on hippocampal glucose levels measured using microdialysis (a decrease associated with glucose pre-treatment in control animals) but not amperometry. There were significant increases in hippocampal oxygen during +-maze exploration. Combining the findings from both methods, it appears that hippocampal activity in the spontaneous alternation task does not cause an increase in glucose consumption, despite an increase in regional cerebral blood flow (using oxygen supply as an index of blood flow) and, as such, pre-treatment with glucose does not enhance spontaneous alternation performance.
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