Metacognitive monitoring and control in visual change detection: Implications for situation awareness and cognitive control.

Metacognitive monitoring and control of situation awareness (SA) are important for a range of safety-critical roles (e.g., air traffic control, military command and control). We examined the factors affecting these processes using a visual change detection task that included representative tactical displays. SA was assessed by asking novice observers to detect changes to a tactical display. Metacognitive monitoring was assessed by asking observers to estimate the probability that they would correctly detect a change, either after study of the display and before the change (judgement of learning; JOL) or after the change and detection response (judgement of performance; JOP). In Experiment 1, observers failed to detect some changes to the display, indicating imperfect SA, but JOPs were reasonably well calibrated to objective performance. Experiment 2 examined JOLs and JOPs in two task contexts: with study-time limits imposed by the task or with self-pacing to meet specified performance targets. JOPs were well calibrated in both conditions as were JOLs for high performance targets. In summary, observers had limited SA, but good insight about their performance and learning for high performance targets and allocated study time appropriately.

Sound localization with head movement: implications for 3-d audio displays.

Previous studies have shown that the accuracy of sound localization is improved if listeners are allowed to move their heads during signal presentation. This study describes the function relating localization accuracy to the extent of head movement in azimuth. Sounds that are difficult to localize were presented in the free field from sources at a wide range of azimuths and elevations. Sounds remained active until the participants' heads had rotated through windows ranging in width of 2, 4, 8, 16, 32, or 64° of azimuth. Error in determining sound-source elevation and the rate of front/back confusion were found to decrease with increases in azimuth window width. Error in determining sound-source lateral angle was not found to vary with azimuth window width. Implications for 3-d audio displays: the utility of a 3-d audio display for imparting spatial information is likely to be improved if operators are able to move their heads during signal presentation. Head movement may compensate in part for a paucity of spectral cues to sound-source location resulting from limitations in either the audio signals presented or the directional filters (i.e., head-related transfer functions) used to generate a display. However, head movements of a moderate size (i.e., through around 32° of azimuth) may be required to ensure that spatial information is conveyed with high accuracy.

Source monitoring and proneness to auditory-verbal hallucinations: a signal detection analysis.

INTRODUCTION: It has been suggested that a bias to misattribute self-generated thoughts to a nonself source underlies the experience of auditory-verbal hallucinations (AVH). We tested this hypothesis with healthy participants prone or not prone to AVH. METHOD: Participants (N=133) were presented with 96 words for subsequent recognition (half positively, half negatively valenced). For self-generated trials, participants generated a sentence containing the word. For other-generated trials, participants heard a prerecorded sentence containing the word. At test, studied words were re-presented visually, intermixed with 96 matched lures. Participants indicated the study status (old or new) and source (self or other) for each item. Sensitivity and bias measures were derived for item and source memory using signal detection theory. The 20 participants scoring highest on questions relating to AVH from the revised Launay-Slade Hallucination Scale formed the high-AVH group and the 20 scoring lowest formed the low-AVH group. RESULTS: ANOVAs revealed no significant differences between the two participant groups in sensitivity or bias of source memory, regardless of item valence. There was a trend for the sensitivity of item memory to be lower in the high-AVH group, compared with the low-AVH group. The bias of item memory was not significantly different between groups. CONCLUSIONS: Although we found no evidence that source-monitoring problems underlie the experience of AVHs in the general population, we recommend that signal detection measures be applied in future investigations of source monitoring in at-risk and clinical populations.

Hearing voices inside and outside the head: spatial source monitoring in participants prone to auditory hallucinations.

INTRODUCTION: Previous studies of source monitoring and auditory hallucinations (AH) have often conflated spatial source (internal-external) with source agency (self-other). Other studies have used suboptimal manipulations of auditory space (e.g., imagine saying vs. saying aloud). We avoided these problems by presenting experimenter-generated stimuli over headphones in the voice of another person so that the location of the voice sounded either internal or external to the participant's head. METHODS: Participants (N=121) studied 96 words and indicated for each whether it was presented internally or externally (online spatial source monitoring). At test, studied words were presented visually, intermixed randomly with 96 unstudied words. Participants indicated whether each item was old or new (item memory) and whether it was presented internally or externally during study (spatial source memory). Independent measures of memory accuracy and response bias were derived for online source monitoring, item memory and source memory using signal detection theory. Performance on these measures was compared between two groups of 30 participants who scored low or high on a measure of AH proneness. RESULTS: ANOVAs revealed no differences between the high- and low-AH groups in online spatial source monitoring, item memory, or spatial source memory. CONCLUSIONS: We found no evidence that proneness to AH in a sample of healthy volunteers was related to any of the measures of spatial source monitoring performance. We recommend that the methods introduced be applied to future investigations of spatial source monitoring with patient groups and with individuals at-risk for psychosis.

Spatial release from speech-on-speech masking in the median sagittal plane.

Several studies have described a release from speech-on-speech masking associated with separation of target and masker sources in the median sagittal plane. Some have excluded the possibility that small differences between target and masker interaural time disparities can fully account for this release. This study explored the mechanisms underlying the spatial release from speech-on-speech masking that can be obtained in the absence of such differences. In one condition, interaural time disparities were removed from the nominal median-sagittal-plane, head-related impulse responses used to generate the virtual auditory space within which competing sentences were presented. In other conditions, interaural level and spectral disparities also were manipulated by presenting competing sentences monaurally or diotically after convolution with one ear's head-related impulse responses. It was found that substantial spatial release from masking can be obtained in the absence of any interaural disparities and that such disparities probably make a relatively minor contribution to spatial release from speech-on-speech masking in the median sagittal plane. It is argued that this release from masking is driven primarily by a reduction in informational masking that occurs when monaural information at one, or both, of the listener's ears facilitates differentiation of competing sentences that emanate from spatially separated sources.

Memory for the locations of environmental sounds.

The accuracy with which a single source of sound can be localized has been examined in many studies, but very few studies have examined the ability of participants to determine the absolute locations of multiple sources of sound. The current study assessed participants' abilities to determine and remember the locations of up to six sources of environmental sound that were positioned at a range of azimuths and elevations in virtual auditory space. In experiment 1, a sequence of one to six sounds was presented one, three, or five times in each trial and the target sound was nominated following presentation of the last sequence. In experiment 2, memory load was held constant by nominating the target sound prior to a single sequence presentation. Localization accuracy was observed to decrease as the number of sounds was increased to three or more under the conditions of experiment 1, but not those of experiment 2. In experiment 1, localization was more accurate when sequences were presented more than once. Pronounced primacy and recency effects were observed for the six sound conditions in experiment 1. An analysis of errors for those conditions indicated that immediate temporal errors, but not immediate spatial errors, were over-represented.

A dual-process account of auditory change detection.

Listeners can be "deaf" to a substantial change in a scene comprising multiple auditory objects unless their attention has been directed to the changed object. It is unclear whether auditory change detection relies on identification of the objects in pre- and post-change scenes. We compared the rates at which listeners correctly identify changed objects with those predicted by change-detection models based on signal detection theory (SDT) and high-threshold theory (HTT). Detected changes were not identified as accurately as predicted by models based on either theory, suggesting that some changes are detected by a process that does not support change identification. Undetected changes were identified as accurately as predicted by the HTT model but much less accurately than predicted by the SDT models. The process underlying change detection was investigated further by determining receiver-operating characteristics (ROCs). ROCs did not conform to those predicted by either a SDT or a HTT model but were well modeled by a dual-process that incorporated HTT and SDT components. The dual-process model also accurately predicted the rates at which detected and undetected changes were correctly identified.

Localization of sound presented via a spatial audio display during visually induced vection in pitch, roll, and yaw.

INTRODUCTION: There is growing interest in the potential application of 3D audio displays to impart spatial information to aircraft pilots. As the aviation environment is dynamic, the effect on sound localization of the visual and vestibular stimulation resulting from motion during flight needs to be assessed. In this study, we investigated whether sound localization is affected by visual cues to self-motion. METHOD: Participants localized bursts of broadband acoustic noise presented from the frontal hemifield under conditions of yaw, pitch, and roll vection (around the z-, y-, and x-axis, respectively) induced by wide-field visual motion of a projected sinusoidal grating. Lateral and elevation components of localization errors were measured. RESULTS: Average signed lateral and elevation errors were less than 1.6 degrees for all vection conditions. The effects of vection condition on lateral and elevation errors were not statistically significant. Also, the interactions between vection condition and sound-source location for these errors were not significant. The magnitudes of the 95% confidence intervals for the differences in lateral and elevation errors between the no-vection condition and each of the other vection conditions did not exceed 3 degrees. CONCLUSION: In the presence of visual cues to yawing, pitching, or rolling self-motion, the perception of auditory space is generally consistent with the available head-centered auditory cues to sound-source location. These results support the application of 3D audio displays in dynamic visual environments such as that experienced during flight.

The role of spatial location in auditory search.

The majority of research findings to date indicate that spatial cues play a minor role in enhancing listeners' ability to parse and detect a sound of interest when it is presented in a complex auditory scene comprising multiple simultaneous sounds. Frequency and temporal differences between sound streams provide more reliable cues for scene analysis as well as for directing attention to relevant auditory 'objects' in complex displays. The present study used naturalistic sounds with varying spectro-temporal profiles to examine whether spatial separation of sound sources can enhance target detection in an auditory search paradigm. The arrays of sounds were presented in virtual auditory space over headphones. The results of Experiment 1 suggest that target detection is enhanced when sound sources are spatially separated relative to when they are presented at the same location. Experiment 2 demonstrated that this effect is most prominent within the first 250 ms of exposure to the array of sounds. These findings suggest that spatial cues may be effective for enhancing early processes such as stream segregation, rather than simply directing attention to objects that have already been segmented.

Sound localisation during illusory self-rotation.

Auditory elevation localisation was investigated under conditions of illusory self-rotation (i.e., vection) induced by movement of wide-field visual stimuli around participants' z-axes. Contrary to previous findings which suggest that auditory cues to sound-source elevation are discounted during vection, we found little evidence that vection affects judgements of source elevation. Our results indicate that the percept of auditory space during vection is generally consistent with the available head-centered auditory cues to source elevation. Auditory information about the head-centered location of a source appears to be integrated, without modification, with visual information about head motion to determine the perceived exocentric location of the source.

Spectral integration time of the auditory localisation system.

For the elevation and front-versus-back hemifield of a sound source to be accurately determined, the sound must contain a broad range of frequencies. Experiment 1 of this study examined the spectral integration time of the auditory localisation system by measuring the accuracy with which frequency-modulated (FM) tones of modulation periods ranging from 0.5 to 200 ms can be localised. For each of the four participants, judgements of sound-source elevation and front-back hemifield were most accurate for a modulation period of 5 ms. Accuracy levels for the 5 ms modulation period approached those for a pink-noise stimulus. This suggests that the spectral integration time of the auditory localisation system is around 5 ms. Supporting evidence for this conclusion was sought in experiment 2, in which two participants localised noise stimuli that had magnitude spectra identical to those of 5 ms equivalent-rectangular-duration samples of the FM tones from experiment 1. For both participants, functions relating localisation error measures (i.e., elevation error and frequency of front-back confusion) to modulation period for spectrally matched noises were similar to those for FM tones.

Spatial audio displays improve the detection of target messages in a continuous monitoring task.

OBJECTIVE: The detection of target messages in a background of competing speech and the identification of the color/number combinations in those messages were examined in a continuous monitoring task. BACKGROUND: Previous research has shown that if listeners know when and where to listen, speech-on-speech intelligibility is improved when signals are presented via a 3-D audio display as compared with a diotic display. However, the effect of display type on detection of infrequent target messages in a continuous monitoring task has not been examined. METHOD: Participants were required to monitor five communications channels conveying messages at random intervals under each of three audio display conditions: diotic, all channels in front, and channels separated in azimuth (3-D). RESULTS: Message detection sensitivity was significantly higher for the 3-D condition than for the in-front condition but did not differ significantly between the in-front and the diotic conditions. There were no differences in response criteria across conditions. Color/number identification sensitivity also was significantly higher for the 3-D condition than for the in-front condition but did not differ significantly between the in-front and the diotic conditions. CONCLUSION: A 3-D audio display enhances both message detection and message identification in a continuous monitoring task. APPLICATION: Three-dimensional audio displays would be particularly beneficial in environments such as aviation, in which the information conveyed to operators via the auditory modality can be crucial to the safe and effective performance of their work.

Learning and retention of associations between auditory icons and denotative referents: implications for the design of auditory warnings.

OBJECTIVE: This study examined the way in which the type and preexisting strength of association between an auditory icon and a warning event affects the ease with which the icon/event pairing can be learned and retained. BACKGROUND: To be effective, an auditory warning must be audible, identifiable, interpretable, and heeded. Warnings consisting of familiar environmental sounds, or auditory icons, have potential to facilitate identification and interpretation. The ease with which pairings between auditory icons and warning events can be learned and retained is likely to depend on the type and strength of the preexisting icon/event association. METHOD: Sixty-three participants each learned eight auditory-icon/denotative-referent pairings and attempted to recall them 4 weeks later. Three icon/denotative-referent association types (direct, related, and unrelated) were employed. Participants rated the strength of the association for each pairing on a 7-point scale. RESULTS: The number of errors made while learning pairings was greater for unrelated than for either related or direct associations, whereas the number of errors made while attempting to recall pairings 4 weeks later was greater for unrelated than for related associations and for related than for direct associations. Irrespective of association type, both learning and retention performance remained at very high levels, provided the strength of the association was rated greater than 5. CONCLUSION: This suggests that strong preexisting associations are used to facilitate learning and retention of icon/denotative-referent pairings. APPLICATION: The practical implication of this study is that auditory icons having either direct or strong, indirect associations with warning events should be preferred.

A test of the magnocellular deficit theory of dyslexia in an adult sample.

An influential theory of dyslexia is based on the premise that individuals with the disorder have impaired sensitivity to rapidly changing stimuli in the visual and auditory modalities, due to a dysfunction in the magnocellular channel of the visual system and its analogue in the auditory pathway. The deficit in the auditory system is thought to cause difficulties in the segmentation of speech and the formation of accurate phonological representations, leading to problems in making the grapheme-phoneme correspondences necessary for reading. In a sample of 13 adults with a history of severe reading difficulty and 18 controls, visual contrast thresholds were measured in response to an 8-Hz flickering Gaussian blob as well as a slowly modulated 8 cycles/deg Gaussian windowed grating. Auditory thresholds were measured in response to a 4-s burst of white noise, the 2nd or 3rd second of which was amplitude modulated at 100 Hz or 1 Hz. The adult reading difficulty group exhibited normal thresholds to rapidly changing stimuli in both modalities and to the slowly modulated visual stimulus, but some showed reduced sensitivity to the 1-Hz amplitude-modulated auditory stimulus. Sensitivity to amplitude modulation at slower rates has been shown to be important for segmentation of the speech stream and so may be implicated in the reading difficulty of the affected individuals. A magnocellular deficit cannot explain this impaired sensitivity, which may be the result of a reduced echoic memory span.

Directed attention eliminates 'change deafness' in complex auditory scenes.

In natural environments that contain multiple sound sources, acoustic energy arising from the different sources sums to produce a single complex waveform at each of the listener's ears. The auditory system must segregate this waveform into distinct streams to permit identification of the objects from which the signals emanate [1]. Although the processes involved in stream segregation are now reasonably well understood [1, 2 and 3], little is known about the nature of our perception of complex auditory scenes. Here, we examined complex scene perception by having listeners detect a discrete change to an auditory scene comprising multiple concurrent naturalistic sounds. We found that listeners were remarkably poor at detecting the disappearance of an individual auditory object when listening to scenes containing more than four objects, but they performed near perfectly when their attention was directed to the identity of a potential change. In the absence of directed attention, this "change deafness" [4] was greater for objects arising from a common location in space than for objects separated in azimuth. Change deafness was also observed for changes in object location, suggesting that it may reflect a general effect of the dependence of human auditory perception on attention.

Localization of virtual sound at 4 Gz.

INTRODUCTION: Acceleration directed along the body's z-axis (Gz) leads to misperception of the elevation of visual objects (the "elevator illusion"), most probably as a result of errors in the transformation from eye-centered to head-centered coordinates. We have investigated whether the location of sound sources is misperceived under increased Gz. METHOD: Visually guided localization responses were made, using a remotely controlled laser pointer, to virtual auditory targets under conditions of 1 and 4 Gz induced in a human centrifuge. As these responses would be expected to be affected by the elevator illusion, we also measured the effect of Gz on the accuracy with which subjects could point to the horizon. RESULTS: Horizon judgments were lower at 4 Gz than at 1 Gz, so sound localization responses at 4 Gz were corrected for this error in the transformation from eye-centered to head-centered coordinates. We found that the accuracy and bias of sound localization are not significantly affected by increased Gz. CONCLUSION: The auditory modality is likely to provide a reliable means of conveying spatial information to operators in dynamic environments in which Gz can vary.

Auditory temporal pattern discrimination and reading ability.

The relation between reading ability and performance on an auditory temporal pattern discrimination task was investigated in children who were either good or delayed readers. The stimuli in the primary task consisted of sequences of tones, alternating between high and low frequencies. The threshold interstimulus interval (ISI) for discrimination of differences in the temporal properties of the sequences was measured. An ISI threshold was also measured in a control task that was identical to the primary task, except all tones in a control sequence had the same frequency. Delayed readers and good readers were equally able to discriminate the timing of the sequences at short ISIs, for both the primary and control tasks. Furthermore, the ISI thresholds were not correlated with the ability to read either irregular words or nonwords. These results suggest that reading ability is not related to the ability to track large and rapid frequency changes in auditory temporal patterns.

Utility of monaural spectral cues is enhanced in the presence of cues to sound-source lateral angle.

The contention that normally binaural listeners can localize sound under monaural conditions has been challenged by Wightman and Kistler (J. Acoust. Soc. Am. 101:1050-1063, 1997), who found that listeners are almost completely unable to localize virtual sources of sound when sound is presented to only one ear. Wightman and Kistler's results raise the question of whether monaural spectral cues are used by listeners to localize sound under binaural conditions. We have examined the possibility that monaural spectral cues provide useful information regarding sound-source elevation and front-back hemifield when interaural time differences are available to specify sound-source lateral angle. The accuracy with which elevation and front-back hemifield could be determined was compared between a monaural condition and a binaural condition in which a wide-band signal was presented to the near ear and a version of the signal that had been lowpass-filtered at 2.5 kHz was presented to the far ear. It was found that accuracy was substantially greater in the latter condition, suggesting that information regarding sound-source lateral angle is required for monaural spectral cues to elevation and front-back hemifield to be correctly interpreted.

Effect of hypobaric hypoxia on auditory sensitivity.

INTRODUCTION: Previous studies on the effect of hypobaric hypoxia on auditory sensitivity are not readily interpretable, in most cases because the potential effect of ambient pressure on stimulus level was not considered. In this study, auditory sensitivity to 1, 8, 12, and 16 kHz tones was compared between conditions of hypoxia and normoxia at the same simulated altitude (3700 m). METHOD: In the hypoxic condition, the partial pressure of oxygen in the inspired air was allowed to decrease with increasing altitude. In the normoxic condition, the partial pressure of oxygen was maintained at a level equivalent to that experienced at mean sea level (MSL). This comparison also controlled for any effect resulting from physiological consequences of hypobaria other than hypoxia (such as a change in middle-ear impedance). RESULTS: A small (2.57 dB) reduction in sensitivity across the frequency range tested was observed. CONCLUSION: A reduction in sensitivity of this magnitude would not be expected to have a large impact on the effectiveness of information transfer via the auditory modality.

The overlay interference task and object-selective visual attention.

A series of experiments was carried out to examine object-based visual attention in an interference task. Observers were presented with two transparently overlapping equilateral triangles forming a "Star of David". One of these triangles was darker than the background, the other was lighter than the background. The observers were required to make a speeded choice response to the orientation of the darker triangle. The presence of the light triangle produced a robust interference effect that manifested as a slower response time. This effect was strongly modulated by the relative contrast of the target and distractor triangles. It was reduced when the light distractor triangle was separated in depth from the target triangle. Since the configuration rules out the possibility of 2-D spatial selection, it is concluded that object-based selection occurs in interference tasks and that the effectiveness of this selection is modulated by visual attributes that are not directly relevant to the task.