The world is filled with richly diverse sounds which we are able to perceptually distinguish using a variety of properties. One of these properties is the amplitude envelope, or the intensity of a sound over time. While it is common in the real world for sounds to have time-varying amplitude envelopes, the majority of sounds used in perceptual research have time-invariant or unspecified amplitude envelopes. The aim of the present thesis is twofold. Because many of the studies using time-invariant or undefined envelopes make use of very short sounds (below 100 msec), the first experiment aimed to determine the duration required for discriminating among three different envelopes: flat (invariant), ramped (increasing in intensity over time), and damped (decreasing in intensity over time). In Experiment 1, participants took part in a 2-alternative forced choice, psychophysical staircase paradigm in which they indicated which of two envelopes they thought they were listening to. Results showed that, when telling ramped tones apart from either flat or damped tones, participants showed discrimination thresholds below 50 msec, while they had thresholds of approximately 75-80 msec when differentiating flat from damped tones. Because amplitude envelope has been shown to impact audiovisual integration and the perceptual system is sensitive to interaural envelope differences when localizing sounds, the second experiment aimed to determine whether amplitude envelope could modulate the visual bias present in spatial ventriloquism, an audiovisual illusion where the perceived location of a sound is influenced by the location of a visual stimulus. In Experiment 2, participants performed a psychophysical staircase task which measured their accuracy in localizing sounds with flat and damped envelopes, with or without a simultaneous flash on the screen in front of them. Results showed that, at durations above the envelope discrimination thresholds found in Experiment 1 (83 msec), there was no visual bias on perceived location of the sound, while the bias was present at a duration below this threshold (16 msec). Together, these results add to the mounting evidence suggesting that amplitude envelope has profound and varied effects on our perception of sounds, and is an important property to consider when designing experiments. / Thesis / Master of Science (MSc)

Amplitude envelope is an important aspect of auditory perception. As one article included (Chapter 3) goes into great detail regarding this, it will not be discussed here. Included are two articles that explore the importance and influence of amplitude envelope in auditory perception research. The first article (Chapter 2) explores the role of amplitude envelope in an associative memory task, with the aim of improving the associability of auditory alarms in medical devices. Although we found no difference in performance based on amplitude envelope, the paper discusses the patterns of incorrect alarm identification and identifies potential sources of confusion. While this was not our initial goal, we feel this article is a valuable contribution that connects two distinct fields: music cognition and alarm design. The second article (Chapter 3) encompasses a meta-analysis, surveying the temporal structure of sounds used in auditory perception research, namely in the journal Attention, Perception & Psychophysics. This articles discusses several studies in which amplitude envelope has categorically influenced experimental outcomes and suggests that the standard ‘flat’ temporal structure (i.e. abrupt onset, period of sustain and abrupt offset) may not be the best way to evaluate the auditory system. The goal of this article is to determine what proportion of studies are using the standard ‘flat’ tones vs. other types of temporal structures we may encounter during everyday listening. These two articles collectively illustrate the original research I have completed on amplitude envelope during my Master’s Degree. / Thesis / Master of Science (MSc)

Auditory alarm annoyance plagues clinicians, which results in alarms desensitization and ultimately affects patient care. Contributing to this problem are the International Electrotechnical Commission (IEC) 60601-1-8 alarms, a standardized set of melodic alarms used to convey information to clinicians in intensive care units. By design, IEC alarms employ flat amplitude (i.e., amplitude invariant) envelopes and are not reflective of naturally occurring sounds with percussive amplitude (i.e., decaying) envelopes. We present a series of three experiments evaluating the effect of amplitude envelope manipulation (i.e., incorporating percussive envelope) on memory and annoyance in IEC alarms synthesized using pure tones (experiment 1), complex tones (experiment 2) and assessing annoyance pre and post memory assessment (experiment 3). For the memory assessment, participants were assigned to learn either the flat alarms or percussive alarms. During the memory assessment, participants were informed of the alarm–referent pairings (study phase), practised identifying alarms (training phase), had a short break, and tested on their ability to identify alarms (evaluation phase). The annoyance assessment was a two alternative forced choice task where participants identified which alarm they perceived to be more annoying from a pair of alarms differing in either envelope-type or alarm-type. Across all experiments there was no difference in alarm learnability between those learning either flat or percussive alarms during the memory assessment. Annoyance assessments revealed that all participants chose the flat alarms to be more annoying than the percussive alarms, independent of the memory assessment condition. These results showcase the potential of using percussive alarms to reduce alarm annoyance without harming learnability, a cost-efficient manipulation. / Thesis / Master of Science (MSc) / Alarms in intensive care units are perceived as annoying, ultimately negatively affecting both clinicians and patients. These alarms are mandated by the International Electrotechnical Commission to have sustained or flat amplitude envelopes (i.e., referring to the change in loudness over time), which does not reflect naturally occurring stimuli that typically have decaying or percussive amplitude envelopes. The current experiments assessed the effect of percussive envelopes on alarm learnability and annoyance. We showed in a series of experiments that there is no difference in learning alarms with flat or percussive envelopes. However, we showed that alarms with percussive envelopes are perceived to be less annoying than alarms with flat envelopes. These results offer one potential solution to reduce alarm annoyance in intensive care units without harming the learnability of these alarms.