Assessing working memory capacity through picture span and feature binding with visual-graphic symbols during a visual search task with typical children and adults.

This study investigated developmental memory capacity through picture span and feature binding. Participants included third grade students and college age adults with typical development. Picture span was used to assess working memory capacity when participants were asked to identify, locate, and sequence common visual-graphic symbols from experimental grid displays. Feature binding was assessed to evaluate how symbols, locations and sequences are bound together in working memory. The features assessed included symbol recall, location recall, symbol location binding, symbol sequence binding, and location sequence binding. All participants were shown a sequence of visual-graphic symbols on 4 by 4 stimulus grid displays. Participants were then asked to remember symbols amidst distractor symbols and place them in the correct location on a response grid, using the correct sequence. Results revealed expected developmental differences between third graders and adults on picture span. Significant differences between third graders and adults were also obtained for symbol sequence and location sequence binding. Performance for both groups on the sequence binding features were marginal (i.e., 30% of third graders and 60% of adults binding symbol sequence; 27% of third graders and 52% of adults binding location sequence). These results convey the influence of picture span and feature binding on working memory capacity. Implications are discussed in relation to theoretical models on working memory and compensatory strategies to increase feature binding with target and contextual memory.

DPOAE component estimates and their relationship to hearing thresholds.

Distortion product otoacoustic emissions (DPOAEs) recorded in the ear canal are a composite or vector sum of two underlying components. The relationship between hearing thresholds and DPOAE-component level, rather than composite level, has been of recent interest. Two different signal-processing methods, inverse fast Fourier transform (IFFT) with time-windowing and low-pass filtering, were used to obtain estimates of the levels of the two components. Component estimates were then correlated to behavioral thresholds. Improvement in the strength of the correlation was not significant over that of the composite. While the signal processing methods were found to yield similar estimates of the generation component, application of the IFFT with time-windowing method was more complex due to the overlap of the components in the time domain. This time domain variability was observed both within and between subjects. These results highlight the complexities of DPOAE generation and the related difficulties of component separation.

Generation of DPOAEs in the guinea pig.

In humans, distortion product otoacoustic emissions (DPOAEs) at frequencies lower than the f(2) stimulus frequency are a composite of two separate sources, these two sources involving two distinctly different mechanisms for their production: non-linear distortion and linear coherent reflection [Talmadge et al., J. Acoust. Soc. Am. 104 (1998) 1517-1543; Talmadge et al., J. Acoust. Soc. Am. 105 (1999) 275-292; Shera and Guinan, J. Acoust. Soc. Am. 105 (1999) 332-348; Kalluri and Shera, J. Acoust. Soc. Am. 109 (2001) 662-637]. In rodents, DPOAEs are larger, consistent with broader filters; however the evidence for two separate mechanisms of DPOAE production as seen in humans is limited. In this study, we report DPOAE amplitude and phase fine structure from the guinea pig with f(2)/f(1) held constant at 1.2 and f(2) swept over a range of frequencies. Inverse Fast Fourier Transform analysis and time-domain windowing were used to separate the two components. Both the 2f(1)-f(2) DPOAE and the 2f(2)-f(1) DPOAE were examined. It was found that, commensurate with human data, the guinea pig DPOAE is a composite of two components arising from different mechanisms. It would appear that the 2f(1)-f(2) emission measured in the ear canal is usually dominated by non-linear distortion, at least for a stimulus frequency ratio of 1.2. The 2f(2)-f(1) DPOAE exhibits amplitude fine structure that, for the animals examined, is predominantly due to the variation in amplitude of the place-fixed component. Cochlear delay times appear consistent with a linear coherent reflection mechanism from the distortion product place for both the 2f(1)-f(2) and 2f(2)-f(1) place-fixed components.

Effects of a suppressor tone on distortion product otoacoustic emissions fine structure: why a universal suppressor level is not a practical solution to obtaining single-generator DP-grams.

OBJECTIVES: The use of a suppressor tone has been proposed as the method of choice in obtaining single-generator distortion product (DP) grams, the speculation being that such DP grams will be more predictive of hearing thresholds. Current distortion product otoacoustic emissions (DPOAE) theory points to the ear canal DPOAE signal being a complex interaction between multiple components. The effectiveness of a suppressor tone is predicted to be dependent entirely on the relative levels of these components. We examine the validity of using a suppressor tone through a detailed examination of the effects of a suppressor on DPOAE fine structure in individual ears. DESIGN: DPOAE fine structure, recorded in 10 normal-hearing individuals with a suppressor tone at 45, 55, and 65 dB SPL, was compared with recordings without a suppressor. Behavioral hearing thresholds were also measured in the same subjects, using 2-dB steps. RESULTS: The effect of the suppressor tone on DPOAE fine structure varied between ears and was dependent on frequency within ears. Correlation between hearing thresholds and DPOAE level measured without a suppressor was similar to previous reports. The effects of the suppressor are explained in the theoretical framework of a model involving multiple DPOAE components. CONCLUSIONS: Our results suggest that a suppressor tone can have highly variable effects on fine structure across individuals or even across frequency within one ear, thereby making the use of a suppressor less viable as a clinical tool for obtaining single-generator DP grams.

What drives mechanical amplification in the mammalian cochlea?

The recent report by Peter Dallos and colleagues of the gene and protein responsible for outer hair cell somatic motility (Zheng, Shen, He, Long, Madison, & Dallos, 2000), and the work of James Hudspeth and colleagues demonstrating that vestibular stereocilia are capable of providing power that may boost the vibration of structures within the inner ear (Martin & Hudspeth, 1999), presents the tantalizing possibility that we may not be far away from answering the question what drives mechanical amplification in the mammalian cochlea? This article reviews the evidence for and against each of somatic motility as the motor, and a motor in the hair cell bundle, producing cochlear mechanical amplification. We consider three models based on somatic motility as the motor and two based on a motor in the hair cell bundle. Available evidence supports a hair cell bundle motor in nonmammals but the upper frequency limit of mammalian hearing in general exceeds that of nonmammals, in many cases by an order of magnitude or more. Only time will tell whether an evolutionary dichotomy exists (Manley, Kirk, Köppl, & Yates, 2001).

Sources and mechanisms of DPOAE generation: implications for the prediction of auditory sensitivity.

Otoacoustic emissions (OAEs) have become a commonly used clinical tool for assessing cochlear health status, in particular, the integrity of the cochlear amplifier or motor component of cochlear function. Predicting hearing thresholds from OAEs, however, remains a research challenge. Models and experimental data suggest that there are two mechanisms involved in the generation of OAEs. For distortion product, transient, and high-level stimulus frequency emissions, the interaction of multiple sources of emissions in the cochlea leads to amplitude variation in the composite ear canal signal. Multiple sources of emissions complicate simple correlations between audiometric test frequencies and otoacoustic emission frequencies. Current research offers new methods for estimating the individual components of OAE generation. Input-output functions and DP-grams of the nonlinear component of the 2f2-f2 DPOAE may ultimately show better correlations with hearing thresholds. This paper reviews models of OAE generation and methods for estimating the contribution of source components to the composite emission that is recorded in the ear canal. The clinical implications of multiple source components are discussed.