Earphone Channels Research Articles

A Joint Power Harvesting and Communication Technology for Smartphone Centric Ubiquitous Sensing Applications

Smartphone centric ubiquitous sensing applications use a smartphone with external sensors. The 3.5mm audio interface provide a common data interface for communication in different smartphones. The 3.5mm audio interface cannot provide DC power to external sensors. Thus, power needs to be harvested from an earphone channel. The existing technology uses one earphone channel to harvest power. Consequently, for many smartphones the technology cannot harvest enough power to support external sensors. In this paper, based on frequency shift keying (FSK) modulation scheme, the authors have proposed a joint power harvesting and communication technology that can simultaneously harvest power and transfer data with the same earphone channels. Circuit measurements show that, the proposed technology can extract more than two times of power as from one earphone channel. Meanwhile, demodulation tests show that our newly-developed timer-based FSK demodulator can reliably recover the data transferred from a smartphone to external sensors without any error.

Extraction of spectral pitch information from auditory patterns as a function of pattern duration

The ability to extract specific pitch information from one tone part of a musical chord might reasonably be expected to depend on the duration of that chord. The purpose of the current study was to explore this relationship. The observer was required to perform a mortaural detection task where the frequency of a signal event was randomly varied from trial to trial. On each trial, a cue matching the frequency of the signal event was presented in the contralateral earphone channel prior to the detection interval. Previous studies in this series have established the observer's ability to use the pitch information from this cue to reinstate detection performance to normal levels. In this study, two variables were manipulated. The first variable was (1) whether the duration of the cue was randomly varied across trims or (2) whether cue duration was varied across blocks of trials but fixed in duration within a block. The second variable was whether the cue was one tone part of a three‐element musical chord or presented alone. A comparison of performance in the resulting four experimental conditions suggests that pitch extraction from auditory patterns is most demanding for pattern durations under 100 ms. However, if an observer knows what pattern duration to expect, extraction of relevant pitch information from the embedded cue can reach the levels realized with the cue presented in isolation, even for short pattern durations.

Critical-band effects in two-channel auditory signal detection.

Two-channel auditory signal detection was investigated with 50-msec sinusoidal signals masked by binaurally uncorrelated noise. In the two-channel tasks, the signals in each earphone channel were presented with an independent probability during the single observation interval and the observers were required to detect the inputs in a single earphone (selective-attention condition) or in both earphones (divided-attention condition). When the signals in each earphone were within the same critical band (the assumed singled processing unit in frequency domain), there was a decrement in detection performance in both the selective- and divided-attention (i.e. dichotic) conditions compared with the monaural condition. However, when signals were separated in frequency by several critical bands, a decrement in dichotic performance, as compared with monaural performance, occurred only in the divided-attention condition. These findings are discussed in terms of their implications regarding models of multichannel signal processing and the definition of input channels in terms of earphones.

Intervening stimulus effects on category judgments of duration

Auditory pulses (1,000 Hz) occurring between the 500-Hz bounding markers of durations being judged were varied in their position and number over three experiments which examined the effects of these factors on measures of amount of filled-duration illusion (FDI) and interduration discriminability. The results establish that the locus of the FDI is postattentive, since some of the incoming sensory information, selected on the basis of simple physical cues, can be excluded from further processing. FDI decreases both when the intervening stimuli come from a different source (earphone channel) to the marker stimuli and when they appear as part of an ongoing sequence of background pulses. Discrimination of durations containing intervening stimuli is enhanced if the filler events are placed such that repetitions of a given subinterval result. Thomas and Brown’s (1974) “chunking” model can account for the observed effects with the additional assumption that the error associated with encoding a given subinterval is sequentially modified as a function of number of recent encodings.

Selective attention. I. Two-channel simultaneous frequency difference limen.

A set of experiments which assesses the ability of human observers to monitor two earphone channels for the purpose of performing one or two independent and simultaneous frequency difference-limen tasks is described. Performance (d′) was significantly poorer with dichotic stimulus presentation than with monaural, control conditions. Under dichotic presentation conditions, performance was equivalent whether the observers were instructed to listen to one or both channels. A detailed analysis of the data indicated that the observers could discriminate a change but seemed to have difficulty in identifying the channel in which the change occurred. Consistent with results reported in the simultaneous signal-detection literature using intensity detection or discriminations, we found that observers cannot successfully monitor more than one channel. It is suggested that when the dichotic stimulus presentation provides useful information which is not present during monaural tasks (i.e., lateralization cues), observers may be able, using this added information, to perform a divided attention task with little or no apparent performance decrement relative to single-channel tasks.

Sequential two-channel frequency difference limen

The ability of trained observers to monitor the sequential inputs to two earphone channels was explored. In the independent same-different frequency discrimination tasks, the two temporally discrete standard stimuli were followed by two temporally discrete comparison stimuli such that the stimulus offset in the first channel was contiguous with the stimulus onset in the second. As with our earlier experiments [Ahroon, Pastore, and Wolz, J. Acoust. Soc. Am. 56, S45 (1974)], one-monaural and two-dichotic (selective-attention and divided-attention) listening conditions, temporal separation of the standard and comparison stimuli facilitated performance in the trailing channel in selective attention tasks, but not in the divided attention tasks. However, performance under both dichotic conditions was significantly poorer than monaural performance, with backward interference more disruptive than forward interference. In addition, the data give no support for a model based on an analogue to a real-time computer-interrupt handling system in two-channel discrimination experiments. [Research supported by a graft from NINDS.]

Attentional factors in simultaneous two-channel auditory signal detection

This study investigated attentional factors involved in two-channel auditory signal detection. The brief 50 msec sinusoidal signals, masked by binaurally uncorrelated, band-limited noise, were presented simultaneously to two separate earphone channels each with an independent probability of 0.5. The two-channel detection tasks required observers to monitor one (selective attention condition) or both (divided attention condition) of the earphone channels. Compared to the single channel condition, observers showed a slight (1–3 dB), but consistent, decrement in detection performance in both the selective and divided attention conditions with signals separated in frequency by less than one critical band (Δf=65 Hz). With signals separated in frequency by more than one critical band (Δf=1565 Hz), observers again showed a slight performance decrement when dividing their attention between two earphone channels, but could effectively monitor one channel while attempting to ignore the other. [This work was supported by a grant from NINDS.]

Selective attention and simple auditory recognition: Methodological considerations

We have reported at recent meetings a severe performance decrement in two-channel frequency difference limen tasks. In these studies, d's in both the selective attention and divided attention conditions were significantly depressed relative to monaural levels. When the signals to the two earphone channels were widely separated in frequency (by nine to ten critical bands), the selective attention condition was improved relative to the divided attention condition, yet still significantly below monaural performance levels. When all signals were within the same critical band (or were separated by only two or three critical bands), there were no significant differences between the two dichotic conditions. The present study generated psychometric functions under the selective and divided attention conditions for signals within the same critical band. Using this procedure, differences between the two dichotic listening conditions are evident in both absolute performance levels and in the psychometric functions. The results of the present experiment clearly indicate the need for greater use of adaptive psychophysical methods in the study of dual channel listening. [Research supported by grant NS 10995 from N.I.N.D.S.]

Simultaneous two-channel frequency difference limen

The ability of trained observers to monitor two channels in a frequency discrimination inclusive OR paradigm was examined, using clearly detectable signals. The various discrimination tasks involved both (1) the simultaneous monitoring and (2) the single-channel monitoring of simultaneous, independently presented signal events in each earphone channel, as well as (3) the monitoring of events restricted to a single fixed channel. The effects of critical bandwidth limitations on the ability of the observer to perform the tasks was explored. The results are compared with those of two-channel detection tasks in which the ability of the observers to perform is effected by signal frequency separation relative to the critical bandwidth.

Two-channel detection of the missing event

Continuing the investigation of two-channel processing mechanisms, this study explored the effect of defining a signal event as a gap in a continuous sinusoid. The two channels were differentiated spatially by earphone channel; temporally by use of contiguous, non-overlapping observation intervals; and spectrally by use of differential, channel signal frequencies. The observer's task was to make two channel-specific, yes-no decisions concerning the presence of signal events. Signal events in each channel were independently determined and occurred with a probability of 0.5. Three two-channel conditions were explored: a pulse condition where signal events were 100-msec sinusoids, a gap condition where signal events were 100-msec gaps in otherwise continuous sinusoids, and a mixed condition where signal events were defined as a gap in one channel but as a pulse in the other. Two-channel performance in each condition was evaluated relative to signal-channel performance (a task where signal events could only occur in one channel). In the gap detection conditions, approximately a 4-dB increase in level was required to equate performance with that of pulse detection conditions. With respect to signal-channel performance, two-channel decrements were greatest in the gap condition, less in the mixed condition, and least in the pulse condition. Two-channel performance in the pulse condition was similar to that obtained in equivalent conditions in earlier studies. Performance was much better in the pulse and gap conditions in the absence of a contralateral signal event. This effect was minimal or absent in the mixed condition.

Simultaneous two-channel signal detection. 3. 630- and 1400-Hz signals.

Performance in a simultaneous two-frequency detection task was studied under monaural and dichotic conditions of signal presentation. In the basic task a 630-Hz tone, a 1400-Hz tone, neither tone, or both tones occurred with equal likelihood on an experimental trial. The observer had to specify which of these events had occured. Performance was examined: (a) when the signal could occur only in the right earphone channel, and (b) when the 630- and 1400-Hz signals were confined, respectively, to the left and right earphone channels. Single-frequency comparison conditions were also run. A performance decrement was observed in both of the two-frequency conditions compared to the single-frequency condition. However, there was no consistent difference between the monaural and dichotic two-frequency conditions. An analysis of the conditional detection probabilities revealed the presence of a cross-frequency interference effect on trials when a signal was present at the other frequency. This effect was sufficient to account for the differences between single-frequency and two-frequency detection performance.

Detection of Time Differences and Level Differences from a Position away from the Median Plane

By the use of an interaural phase difference of 90° a 50-Hz band of noise, centered at 500 Hz was delayed to the right ear by 0.5 msec. The resultant sound was perceived as lying well to the left of the median plane. To this continuous noise was added a signal from the same noise source so arranged in phase that the signal plus masker appeared to lie either inward or outward from the continuous masker. The signal plus masker could also be moved inward or outward by introducing a difference of level into the two earphone channels. Detection of these movements was compared with detection of movements away from the median plane by employing the N0Sπ condition with α=90° to obtain a time difference, or α=0° to obtain a level difference relative to the median plane. The results show that detection of a time difference from a position away from the median plane is inferior to detection of a time difference around the median plane. However, the results for a difference of level showed no such advantage for the median plane; detection was the same from both reference positions. The findings are taken as further indication of the relative independence of the time mechanism and the level mechanism of the auditory nervous system. [Supported in part by a grant from the Public Health Service, National Institute of Neurological Diseases and Stroke.]

Binaural Detection in a Sequential Detection Paradigm

An extension of the work reported by this author at the Washington meeting, the present study examines sequential detection in two frequency regions assigned to separate earphone channels. The observer's task was to make yes-no decisions concerning the presence of a sinusoidal signal in each earphone channel. A sequential ordering of observation intervals between earphone channels existed for all experimental conditions. The frequency region to be monitored in the right ear was always 630 Hz. Eight experimental conditions were formed by varying whether the order of presentation of observation intervals across earphone channels was fixed or random, whether the frequency region assigned to the left ear was at 630 or 1400 Hz, and whether the Gaussian noise background across earphone channels was correlated or uncorrelated. All experimental conditions were evaluated relative to performance in corresponding single-channel conditions. Results observed include: (1) Knowledge of the presentation order of observation intervals had little effect on performance; (2) A much larger decrement in performance relative to single-channel performance was obtained with a correlated noise background when the frequency region assigned to each earphone channel was the same; no such difference existed when the frequency regions were different. (3) Performance in one channel was lower if a signal event occurred in the opposite channel.

Binaural Signal Detection: Independent Signals in Each Channel

An experimental technique described by Eijkman and Vendrik [“Can a Sensory System be Specified by Its Internal Noise?,” J. Acoust. Soc. Amer. 37, 1102–1109 (1965)] is applied to a binaural task involving the detection of simultaneous signals in both ears. In the first observation interval of a modfied 2AFC task, a tone burst Vo is presented to each ear. In the second interval, one of four random events occurs: (1) the tone burst Vo is present in each earphone, (2) Vo is in left, Vo+ΔV in right, (3) Vo+ΔV in left, Vo in right, or (4) Vo+ΔV presented in both phones. The observer is to report which of the four events occurred. Uncorrelated noise is continuously present in each earphone channel. Comparison conditions were run in monaural and Sm-Nu versions of the binaural task. Analysis of the data includes consideration of the facilititative-inhibitory interactions between the channels, and the computed between-channel correlation. For example, hit and false-alarm probabilities in each channel are examined in terms of their dependence on signal and response conditions in the other channel. The results are interpreted in the context of binaural masking and contralateral cueing phenomena.

Effect of Switching Earphone Channels upon the Precision of Centering

The precision of centering a noise signal in the head is improved by switching the earphone channels; either by communicating them, or by switching from a single channel for both ears to one channel for one ear and one for the other. Switching reduces both random errors and bias errors.

Precision of Centering a Sound as a Function of the Interaural Correlation

Using earphone presentation and an electrical lag line for control of interaural time, measurements were made of the subject's variability while attempting to center the sound in his head. This variability is presented as a function of the interaural correlation, which was varied by introducing random noise signals into the two earphone channels. Results show a reduction in precision as the correlation is reduced, but with the subject still doing substantially better than chance with the correlation as low as 0.1.