- Change Detection
The ability to detect changes around us, such as the appearance or disappearance of an object, has far-reaching implications for survival. These processes have received considerable attention in Vision research. In contrast, the processes by which listeners detect the appearance or disappearance of objects in busy acoustic scenes, comprised of many concurrent sources, remain poorly understood. This is surprising because often it is sound that alerts us to important changes in the scene: Hearing is sensitive to a much larger space than the other senses and in many cases we hear change before we see it (for example, somebody entering the room while your back is to the door; Sudden quiet from the kids’ playroom indicating they are up to mischief..). Indeed, the auditory system is commonly assumed to play a key role in the brain’s change-detection network by serving as an ‘early warning device’, rapidly directing attention to new events in the scene.
The present project is classified as ‘basic’ research with the goal of understanding how listeners with normal hearing detect and process change-events (appearance or disappearance of sources) in auditory scenes. The behavioural and functional brain imaging experiments detailed here are designed to systematically explore listeners’ change detection behavior, understand the relevant processes and identify their neural underpinnings: How are object appearance and disappearance events detected? What brain mechanisms are involved? Are change events detected automatically by the brain, even when listeners’ attentional focus is elsewhere? What makes certain change events fundamentally more salient than others? Under what conditions do listeners perform well, and which situations result in reduced performance? In busy scenes, such as those we often face in the environment, behaviourally relevant scene changes often coincide in time with other events. How resilient are the auditory change detection mechanisms to irrelevant events occurring at the same time as the auditory change? Do auditory and visual perturbing events have the same detrimental effect on performance?
These issues are important from the point of view of understanding perception and how the brain analyses and represents the dynamics of our surrounding environment. Furthermore, understanding what makes certain events pop out and grab attention, while other events go unnoticed is important for designing human-computer interfaces, and other devices intended to help professionals (operating room personnel, air traffic controllers, pilots, etc.) operate effectively in environments where the detection of change is critical. Additionally, since change detection is a major contributor to efficient interaction with the environment, understanding the profile of change detection in normal listeners can provide a measure against which to evaluate hearing impairment as well as the benefit obtained from hearing aids.
- Detecting and representing patterns in sound sequences
Sounds we encounter in the environment are often patterned (regularly repeating). Accumulating evidence suggests that listeners are very sensitive to these patterns. In Many cases the auditory brain acquires this structure automatically, independent of listeners’ attentional state, supported by automatic mechanisms which are continually searching for regularities within the incoming stimulus and use those to predict future input. These models, or rules, about how sources in the environment are expected to behave, thus constitute a dynamically evolving perceptual model of the acoustic scene. In several ongoing projects, which are examining different forms of patterning and different listening contexts. We are interested in identifying what features of sounds we are sensitive to, how quickly these are learnt, and how this learning is affected by listeners’ attentional and perceptual state. Delineating the operational limits of these mechanisms is essential to uncovering the neural computations which underlie sensitivity to sound patterns, and, more broadly, critical to our understanding of how the dynamics of our acoustic environment are coded by the brain in the course of scene perception.
- Figure ground segregation
An issue at the forefront of research into auditory processing is understanding how listeners perform figure-ground segregation. How are we able to extract, and focus attention on a sound of interest in a background of other interfering sounds (e.g. the voice of a friend in a noisy party)? Our experiments aim to understand how these processes are carried out by listeners, which aspects of sound our brains use to achieve segregation, and the neural systems involved in this process.
Our work approaches the issue of attention from two angles:
- Experiments designed to uncover the neural underpinnings and perceptual limits of selective attention: what aspects of sound can listeners attend to and the brain mechanisms involved in this process. What enables us to perceptually pull out a sound of interest out of a mixture of many sounds (‘the cocktail party problem’)? How is how we listen, affect the way sounds are processed by the brain?
- Experiments aiming to understand what aspects of auditory processing are susceptible to attentional manipulation. I.e. which processes are automatic, and which require attention or are affected by the perceptual state and behavioural goals of the listener. Understanding these processes is important for understanding what information the brain extracts of the auditory world when our focus of attention is diverted away from ‘listening’.
This project aims to understand and quantify auditory salience and distraction in the context of complex acoustic scenes. Namely, the neural and computational processes by which concurrently presented sounds compete for, and capture, listeners’ perceptual and attentional resources. It is widely assumed that the auditory system plays a critical role in the brain’s ‘early warning system’ by continuously scanning the unfolding acoustic scene for potentially relevant events (e.g. the approach of predators or pray) even when attention is focused elsewhere. Characterizing those acoustic features that attract attention is thus an important aspect of studying auditory perception in the healthy brain, as well as for understanding how the system breaks down as a consequence of aging, hearing impairment or certain neurological disorders (e.g. Schizophrenia) which are characterized by abnormal auditory processing. Understanding acoustic salience, and its reverse – distraction, also has immediate applications in guiding the design of warning systems, hearing aids, human computer interfaces, and other devices intended to help individuals respond efficiently to urgent events in their surroundings.
- COgnitive COntrol of a Hearing Aid (COCOHA project)
See project Website