Michael J. Hautus

Corrections for extreme proportions and their biasing effects on estimated values ofd

Estimatingd′ from extreme false-alarm or hit proportions (p = 0 orp = 1) requires the use of a correction, because thez score of such proportions takes on infinite values. Two commonly used corrections are compared by using Monte-Carlo simulations. The first is the 1/(2N) rule for which an extreme proportion is corrected by this factor befored′ is calculated. The second is the log-linear rule for which each cell frequency in the contingency table is increased by 0.5 irrespective of the contents of each cell. Results showed that the log-linear rule resulted in less biased estimates ofd′ that always underestimated populationd′. The 1/(2N) rule, apart from being more biased, could either over- or underestimate populationd′.

Interpreting the effects of response bias on remember-know judgments using signal detection and threshold models

In recognition memory experiments, the tendency to identify a test item as “old” or “new” can be increased or decreased by instructions given at test. The effect of such response bias on remember-know judgments is to change “remember” as well as “old” responses. Existing models of the remember-know paradigm (based on dual-process and signal detection theories) interpret this effect as a shift in response criteria, but differ on the nature of the dimension along which the changes take place. We extended the models to account simultaneously for remember-know and confidence rating data and tested them using old-new (Experiment 1) and remember-know (Experiment 2) rating designs. Quantitative fits show that the signal detection models provide the best overall description of the data.

Object-related brain potentials associated with the perceptual segregation of a dichotically embedded pitch.

The cortical mechanisms of perceptual segregation of concurrent sound sources were examined, based on binaural detection of interaural timing differences. Auditory event-related potentials were measured from 11 healthy subjects. Binaural stimuli were created by introducing a dichotic delay of 500-ms duration to a narrow frequency region within a broadband noise, and resulted in a perception of a centrally located noise and a right-lateralized pitch (dichotic pitch). In separate listening conditions, subjects actively discriminated and responded to randomly interleaved binaural and control stimuli, or ignored random stimuli while watching silent cartoons. In a third listening condition subjects ignored stimuli presented in homogenous blocks. For all listening conditions, the dichotic pitch stimulus elicited an object-related negativity (ORN) at a latency of about 150-250 ms after stimulus onset. When subjects were required to actively respond to stimuli, the ORN was followed by a P400 wave with a latency of about 320-420 ms. These results support and extend a two-stage model of auditory scene analysis in which acoustic streams are automatically parsed into component sound sources based on source-relevant cues, followed by a controlled process involving identification and generation of a behavioral response.

Toward a complete decision model of item and source recognition

In a recognition memory test, subjects may be asked to decide whether a test item is old or new (item recognition) or to decide among alternative sources from which it might have been drawn for study (source recognition). Confidence-rating-based receiver operating characteristic (ROC) curves for these superficially similar tasks are quite different, leading to the inference of correspondingly different decision processes. A complete account of source and item recognition will require a single model that can be fit to the entire data set. We postulated a detection-theoretic decision space whose dimensions, in the style of Banks (2000), are item strength and the relative strengths of the two sources. A model that assumes decision boundaries of constant likelihood ratios, source guessing for unrecognized items, and nonoptimal allocation of attention can account for data from three canonical data sets without assuming any processes specifically devoted to recollection. Observed and predicted ROCs for one of these data sets are given in the article, and ROCs for the other two may be downloaded from the Psychonomic Society’s Archive of Norms, Stimuli, and Data, www.psychonomic.org/archive.

Neural activity associated with binaural processes for the perceptual segregation of pitch

OBJECTIVE We measured late cortical potentials in a psychophysical procedure for binaural unmasking of a dichotically-embedded pitch. METHODS Late-latency auditory evoked potentials were measured from 128 recording channels in 13 healthy subjects. Control stimuli consisted of 500 ms segments of broadband acoustic noise presented identically to both ears via earphones, evoking a perception of noise localized in the centre of the head. Dichotic pitch stimuli were created by introducing a dichotic delay to a narrow frequency region of the same noise segments, and resulted in a perception of both the centrally-located noise and a right-lateralized pitch. RESULTS Both stimuli evoked late auditory event-related potentials (ERPs) characterized by a P1-N1-P2 complex of waves between 60 and 180 ms after stimulus onset. ERPs associated with the control and dichotic pitch stimuli showed no amplitude differences for the P1 and N1 waves. ERPs to dichotic pitch stimuli became significantly more negative beginning at a latency around 150 ms, an effect that was maximal between 210 and 280 ms. Topographic mapping showed that this late negativity was lateralized to the left hemisphere. CONCLUSIONS The late negative wave elicited by the dichotic pitch stimulus reflects neural processing that is dependent upon binaural fusion within the auditory system. SIGNIFICANCE The dichotic pitch paradigm may provide a useful tool for the electrophysiological assessment and study of the temporal processing capabilities of the auditory system. This paradigm may also be useful for the study of binaural mechanisms for the perceptual segregation of concurrent sound sources.

Processing of binaural spatial information in human auditory cortex: neuromagnetic responses to interaural timing and level differences.

This study was designed to test two hypotheses about binaural hearing: (1) that binaural cues are primarily processed in the hemisphere contralateral to the perceived location of a sound; and (2) that the two main binaural cues, interaural timing differences and interaural level differences, are processed in separate channels in the auditory cortex. Magnetoencephalography was used to measure brain responses to dichotic pitches--a perception of pitch created by segregating a narrow band of noise from a wider band of noise--derived from interaural timing or level disparities. Our results show a strong modulation of interhemispheric M100 amplitudes by ITD cues. When these cues simulated source presentation unilaterally from the right hemispace, M100 amplitude changed from a predominant right hemisphere pattern to a bilateral pattern. In contrast, ILD cues lacked any capacity to alter the right hemispheric distribution. These data indicate that intrinsic hemispheric biases are large in comparison to any contralaterality biases in the auditory system. Importantly, both types of binaural cue elicited a circa 200 ms latency object-related negativity component, believed to reflect automatic cortical processes involved in distinguishing concurrent auditory objects. These results support the conclusion that ITDs and ILDs are processed by distinct neuronal populations to relatively late stages of cortical processing indexed by the M100. However information common to the two cues seems to be extracted for use in a subsequent stage of auditory scene segregation indexed by the object related negativity. This may place a new bound on the extent to which sound location cues are processed in separate channels of the auditory cortex.

Relativity of Judgements about Sound Amplitude and the Asymmetry of the Same-Different ROC:

The problem of deciding whether two things are the same or different in magnitude can be solved by judging one magnitude relative to the other, or by making absolute judgements about the magnitude of each. The shape of the resulting receiver operating characteristic depends on which solution is adopted. In order to obtain empirical receiver operating characteristics, we therefore had subjects rate their confidence that two tone amplitudes were the same or different. Four subjects each made 500 ratings of three differences in amplitude. The asymmetry in the obtained characteristics indicated that subjects made relative rather than absolute judgements of the amplitudes, despite the fact that making absolute judgements would lead to better performance on the task.

Lateralized auditory brain function in children with normal reading ability and in children with dyslexia

We examined central auditory processing in typically- and atypically-developing readers. Concurrent EEG and MEG brain measurements were obtained from a group of 16 children with dyslexia aged 8-12 years, and a group of 16 age-matched children with normal reading ability. Auditory responses were elicited using 500ms duration broadband noise. These responses were strongly lateralized in control children. Children with dyslexia showed significantly less lateralisation of auditory cortical functioning, and a different pattern of development of auditory lateralization with age. These results provide further evidence that the core neurophysiological deficit of dyslexia is a problem in the balance of auditory function between the two hemispheres.

CALCULATING ESTIMATES OF SENSITIVITY FROM GROUP DATA: POOLED VERSUS AVERAGED ESTIMATORS

Two methods of estimating the value of populationd′ from a group of subjects were investigated to determine the conditions under which each would be the less biased estimator. The first method, calculatingd′ for each subject and then averaging the estimates, yields an estimate of populationd′ called averaged′. The second method requires that data from all subjects be pooled and then an estimate of populationd′ calculated. This estimator is called pooledd′. Monte Carlo simulations indicated that pooledd′ was the less biased estimator when the number of trials per subject was fairly low, whereas averaged′ was the less biased estimator when the number of trials per subject was fairly high. The crossover point at which averaged′ becomes less biased than pooledd′ is shown to depend on the value of populationd′, the average bias of subjects in the population, and also on the level of criterion variability within the population.

Likelihood-ratio decision strategy for independent observations in thesame-different task: An approximation to the detection-theoretic model

An optimal decision strategy for deciding whether two things are the same or different is to adopt a likelihood-ratio criterion. The parametric equations for the receiver operating characteristic (ROC) based on the likelihood-ratio strategy when observations are independent are complicated; they require the numerical evaluation of a double integral. An approximation to the parametric equations for the likelihood-ratio strategy was developed. This approximation takes the form of a pair of equations that describe ROCs virtually indistinguishable from those of the full model.