Melissa K. Gregg

Attention, awareness, and the perception of auditory scenes.

Auditory perception and cognition entails both low-level and high-level processes, which are likely to interact with each other to create our rich conscious experience of soundscapes. Recent research that we review has revealed numerous influences of high-level factors, such as attention, intention, and prior experience, on conscious auditory perception. And recently, studies have shown that auditory scene analysis tasks can exhibit multistability in a manner very similar to ambiguous visual stimuli, presenting a unique opportunity to study neural correlates of auditory awareness and the extent to which mechanisms of perception are shared across sensory modalities. Research has also led to a growing number of techniques through which auditory perception can be manipulated and even completely suppressed. Such findings have important consequences for our understanding of the mechanisms of perception and also should allow scientists to precisely distinguish the influences of different higher-level influences.

Change Deafness and the Organizational Properties of Sounds.

Change blindness, or the failure to detect (often large) changes to visual scenes, has been demonstrated in a variety of different situations. Failures to detect auditory changes are far less studied, and thus little is known about the nature of change deafness. Five experiments were conducted to explore the processes involved in change deafness by measuring explicit change detection as well as auditory object encoding. The experiments revealed that considerable change deafness occurs, even though auditory objects are encoded quite well. Familiarity with the objects did not affect detection or recognition performance. Whereas spatial location was not an effective cue, fundamental frequency and the periodicity/aperiodicity of the sounds provided important cues for the change-detection task. Implications for the mechanisms responsible for change deafness and auditory sound organization are discussed.

The importance of semantics in auditory representations.

The purpose of the present study was to examine the nature of auditory representations by manipulating the semantic and physical relationships between auditory objects. On each trial, listeners heard a group of four simultaneous sounds for 1 sec, followed by 350 msec of noise, and then either the same sounds or three of the same plus a new one. Listeners completed a change-detection task and an object-encoding task. For change detection, listeners made a same-different judgment for the two groups of sounds. Object encoding was measured by presenting probe sounds that either were or were not present in the two groups. In Experiments 1 and 3, changing the target to an object that was acoustically different from but semantically the same as the original target resulted in more errors on both tasks than when the target changed to an acoustically and semantically different object. In Experiment 2, comparison of semantic and acoustic effects demonstrated that acoustics provide a weaker cue than semantics for both change detection and object encoding. The results suggest that listeners rely more on semantic information than on physical detail.)

Memory for sound, with an ear toward hearing in complex auditory scenes

An area of research that has experienced recent growth is the study of memory during perception of simple and complex auditory scenes. These studies have provided important information about how well auditory objects are encoded in memory and how well listeners can notice changes in auditory scenes. These are significant developments because they present an opportunity to better understand how we hear in realistic situations, how higher-level aspects of hearing such as semantics and prior exposure affect perception, and the similarities and differences between auditory perception and perception in other modalities, such as vision and touch. The research also poses exciting challenges for behavioral and neural models of how auditory perception and memory work.

Enhanced sensory processing accompanies successful detection of change for real-world sounds

Change deafness is the inability of listeners to detect changes occurring in their auditory environment. It is a matter of some debate whether change deafness occurs because of a failure of auditory-specific processes or a failure of more general semantic/verbal memory. To address this issue, we measured event-related potentials (ERPs) to pairs of scenes consisting of naturalistic auditory objects while listeners made a same/different judgment for scenes presented before and after an interruption. ERPs to the post-change scene revealed an enhanced early sensory response (N1) and an enhanced late positivity (P3) for detected changes. Change detection performance was better when there was a large acoustic spread among the objects within Scenes 1 and 2, suggesting that the deficits reflected by the ERP components during change deafness are related to successfully segregating the pre- and post-change objects. We also found that a separate sensory response (P2) reflects implicit, unconscious change detection. Overall, the results provide evidence that auditory-specific sensory processing is critical for both explicit and implicit change detection in natural auditory scenes.

Change deafness and object encoding with recognizable and unrecognizable sounds.

Change deafness is the failure to notice changes in an auditory scene. In this study, we sought to determine if change deafness is a perceptual error, rather than only a reflection of verbal memory limitations. We also examined how successful encoding of objects within a scene is related to successful detection of changes. Event-related potentials (ERPs) were recorded while listeners completed a change-detection and an object-encoding task with scenes composed of recognizable sounds or unrecognizable temporally scrambled versions of the recognizable sounds. More change deafness occurred for the unrecognizable, compared to recognizable sounds, indicating that change deafness is a perceptual error and not solely a product of verbal memory. ERPs from both the recognizable and unrecognizable scenes revealed an enhanced P3b (at PZ/1/2, POZ/3/4 from 350 to 750ms) to detected changes, a marker that conscious change detection has occurred. Recognizable scenes resulted in an enhanced T400 (at T8/TP8, C6/CP6 from 315 to 660ms) to detected changes, possibly indicating activation of established memory representations. Unrecognizable scenes elicited an enhanced P3a (at FCZ/1/2 from 280 to 600ms) to detected changes, indicating enhanced orienting to acoustic change. Performance on the object-encoding task revealed that change deafness was reduced, but not eliminated, when performance on the object-encoding task was accurate.

Effects of capacity limits, memory loss, and sound type in change deafness

Change deafness, the inability to notice changes to auditory scenes, has the potential to provide insights about sound perception in busy situations typical of everyday life. We determined the extent to which change deafness to sounds is due to the capacity of processing multiple sounds and the loss of memory for sounds over time. We also determined whether these processing limitations work differently for varying types of sounds within a scene. Auditory scenes composed of naturalistic sounds, spectrally dynamic unrecognizable sounds, tones, and noise rhythms were presented in a change-detection task. On each trial, two scenes were presented that were same or different. We manipulated the number of sounds within each scene to measure memory capacity and the silent interval between scenes to measure memory loss. For all sounds, change detection was worse as scene size increased, demonstrating the importance of capacity limits. Change detection to the natural sounds did not deteriorate much as the interval between scenes increased up to 2,000 ms, but it did deteriorate substantially with longer intervals. For artificial sounds, in contrast, change-detection performance suffered even for very short intervals. The results suggest that change detection is generally limited by capacity, regardless of sound type, but that auditory memory is more enduring for sounds with naturalistic acoustic structures.

Experience and information loss in auditory and visual memory.

Recent studies show that recognition memory for sounds is inferior to memory for pictures. Four experiments were conducted to examine the nature of auditory and visual memory. Experiments 1–3 were conducted to evaluate the role of experience in auditory and visual memory. Participants received a study phase with pictures/sounds, followed by a recognition memory test. Participants then completed auditory training with each of the sounds, followed by a second memory test. Despite auditory training in Experiments 1 and 2, visual memory was superior to auditory memory. In Experiment 3, we found that it is possible to improve auditory memory, but only after 3 days of specific auditory training and 3 days of visual memory decay. We examined the time course of information loss in auditory and visual memory in Experiment 4 and found a trade-off between visual and auditory recognition memory: Visual memory appears to have a larger capacity, while auditory memory is more enduring. Our results indicate that visual and auditory memory are inherently different memory systems and that differences in visual and auditory recognition memory performance may be due to the different amounts of experience with visual and auditory information, as well as structurally different neural circuitry specialized for information retention.

Change deafness with recognizable and unrecognizable sounds

Change Deafness with Recognizable and Unrecognizable Sounds Change deafness is the remarkably frequent inability of listeners to detect changes occurring in their auditory environment. In this study, we used behavioral measures and event-related potentials (ERPs) to determine if change deafness is a fundamental auditory sensory process, rather than simply a reflection of verbal or semantic memory limitations. Change detection performance was examined for scenes composed of four recognizable or unrecognizable sounds. Listeners completed a change detection task by making a same/different judgment for two consecutively presented scenes that were either the same (Same trials) or had one sound replaced by another sound (Change trials). The behavioral data indicated substantial change deafness for both recognizable and unrecognizable sounds, indicating that change deafness is not the result of verbal or semantic memory limitations. In Change trials, N1 ERPs were less smaller in the post-change scene on trials in which the change was not detected, suggesting that change deafness is associated with less robust sensory encoding. P3 ERPs to the post-change scene were also smaller for non-detected changes, which may reflect lack of memory updating, attention, and/or awareness during change deafness. Overall, the results provide novel information regarding the stages of processing involved in change deafness in natural auditory scenes.

Change deafness and how the auditory system organizes sounds

Change blindness, or the failure to detect changes to a visual scene that seem blatantly obvious after the fact, has been demonstrated in a variety of different situations. Exploration of auditory failures to detect change has been far less studied, even though demonstrations of change deafness could have important theoretical implications. Four experiments were conducted to explore the processes involved in change deafness by measuring explicit change detection as well as auditory object encoding of natural auditory scenes. Considerable change deafness occurred, even though auditory objects were encoded quite well. Change detection performance was better when stimuli were not presented at distinct spatial locations (experiment 1) than when they were presented with spatial cues (experiment 2). Familiarity with the objects did not affect detection or recognition performance. In order to establish an effective cue for auditory detection and recognition, performance was assessed when auditory stimuli were pr...