Adaptive Psychophysical Procedure Research Articles

Spatiotemporal defocus sensitivity function of the human visual system.

Tunable lenses make it possible to measure visual sensitivity to rapid changes in optical power, surpassing the limits imposed by mechanical elements. Using a tunable lens system, we measured, for the first time, the spatiotemporal defocus sensitivity function (STDSF), and the limits of human defocus perception. Specifically, we measured defocus sensitivity using a QUEST adaptive psychophysical procedure for different stimuli (Gabor patches of different spatial frequencies, natural images, and edges) and we developed descriptive models of defocus perception. For Gabor patches, we found on average (across seven subjects) that the maximum sensitivity to defocus is 0.22 D at 14 cpd and 10 Hz, and that the upper limits of sensitivity are 40 cpd and 40 Hz. Our results suggest that accommodation remains fixed while performing the defocus flicker-detection task. These results have implications for new technologies whose working principles make use of fast changes to defocus.

Vibration perception thresholds of human vital and nonvital maxillary incisors

ObjectiveVibrations applied to human teeth have been shown to induce vibrotactile sensations although the location of the mechanoreceptors responsible for encoding vibrations is unclear. The aim of this study is to test the hypothesis that vibrotactile tooth sensations depend on afferent input from intradental mechanoreceptors. DesignVibration perception thresholds were determined for a vital (control) and a contralateral nonvital (endodontically treated) maxillary incisor in 11 healthy human participants using an adaptive psychophysical procedure. An electromechanical vibrator was used to deliver sinusoidal vibrations at 10 frequencies between 40 and 315 Hz. ResultsThe median force thresholds ranged between 41 and 215 mN for vital and 71 and 507 mN for nonvital incisors. Nonvital median force thresholds were significantly higher than vital thresholds at all frequencies between 40 and 315 Hz. A linear regression analysis revealed a significant increase in vibrotactile thresholds with increasing frequency for only the vital incisors. ConclusionsThe results support the hypothesis that mechanoreceptors located within the tooth contribute to vibrotactile tooth sensations and that mechanosensory information from both periodontal ligament and intradental mechanoreceptors facilitates the accurate assessment of food textures during mastication.

Critical Repetition Rates for Perceptual Segregation of Time-Varying Auditory, Visual and Vibrotactile Stimulation

Abstract What sound quality has led to exclude infrasound from sound in the conventional hearing range? We examined whether temporal segregation of pressure pulses is a distinctive property and evaluated this perceptual limit via an adaptive psychophysical procedure for pure tones and carriers of different envelopes. Further, to examine across-domain similarity and individual covariation of this limit, here called the critical segregation rate (CSR), it was also measured for various periodic visual and vibrotactile stimuli. Results showed that sequential auditory or vibrotactile stimuli separated by at least ~80‒90 ms (~11‒12-Hz repetition rates), will be perceived as perceptually segregated from one another. While this limit did not statistically differ between these two modalities, it was significantly lower than the ~150 ms necessary to perceptually segregate successive visual stimuli. For the three sensory modalities, stimulus periodicity was the main factor determining the CSR, which apparently reflects neural recovery times of the different sensory systems. Among all experimental conditions, significant within- and across-modality individual CSR correlations were observed, despite the visual CSR (mean: 6.8 Hz) being significantly lower than that of both other modalities. The auditory CSR was found to be significantly lower than the frequency above which sinusoids start to elicit a tonal quality (19 Hz; recently published for the same subjects). Returning to our initial question, the latter suggests that the cessation of tonal quality — not the segregation of pressure fluctuations — is the perceptual quality that has led to exclude infrasound (sound with frequencies < 20 Hz) from the conventional hearing range.

Reliability of Vestibular Perceptual Threshold Testing About the Yaw Axis.

Vestibular reflexes have traditionally formed the cornerstone of vestibular evaluation, but perceptual tests have recently gained attention for use in research studies and potential clinical applications. However, the unknown reliability of perceptual thresholds limits their current importance. This is addressed here by establishing the test-retest reliability of vestibular perceptual testing. Perceptual detection thresholds to earth-vertical, yaw-axis rotations were collected in 15 young healthy people. Participants were tested at two time intervals (baseline, 5 to 14 days later) using an adaptive psychophysical procedure. Thresholds to 1 Hz rotations ranged from 0.69 to 2.99°/s (mean: 1.49°/s; SD: 0.63). They demonstrated an excellent intraclass correlation (0.92; 95% confidence interval: 0.77 to 0.97) with a minimum detectable difference of 0.45°/s. The excellent test-retest reliability of perceptual vestibular testing supports its use as a research tool and motivates further exploration for its use as a novel clinical technique.

The Moderation Effect of Processing Efficiency on the Relationship Between Visual Working Memory and Chinese Character Recognition.

To investigate the underlying mechanism of the relationship between visual working memory (VWM) and Chinese character recognition, and the moderation effect of processing efficiency on this relationship, 154 first-grade students were administered a battery of tasks for VWM, rapid temporal processing, and Chinese character reading. In the VWM task, the children were asked to remember the jumping routes of a frog and report these routes in reverse sequence. The longest span for which each participant could respond correctly at least four times out of six was the VWM index. In the task of temporal order judgement, the participants were asked to select which of two balls was presented first, with stimulus onset asynchronies varying from 8 to 492 ms according to an adaptive psychophysical procedure. Visual temporal order threshold (VTOT) was utilized as an indicator of processing efficiency. The participants were asked to read 100 characters aloud to measure their word-level reading abilities in Chinese character recognition. After controlling age, non-verbal intelligence, visual short-term memory, morphological awareness, and orthographic awareness, the results of a moderation effect analysis showed that (1) both VWM and visual VTOT predicted Chinese character reading, and (2) the moderation effect of VTOT on the VWM-reading link was significant (p = 0.001). The correlation between VWM and Chinese character reading was positive and significant when VTOTs were above average (i.e., smaller than 87.14 ms); however, the correlation was negative at relatively poor levels of VTOTs (i.e., larger than 231.44 ms).

POWTARZALNOŚĆ TEST–RETEST RÓŻNYCH POMIARÓW PSYCHOAKUSTYCZNYCH PRZY UŻYCIU PROCEDURY NAJWIĘKSZEGO PRAWDOPODOBIEŃSTWA

ObjectivePsychoacoustic abilities include the perception of frequency, intensity, and the temporal parameters of sound, which are necessary for speech perception. These abilities can be measured using adaptive and non-adaptive procedures. The maximum likelihood procedure (MLP) is an adaptive psychophysical procedure that is usually utilized in psychoacoustic tasks. The present study aimed to assess the testretest reliability of various psychoacoustic measures assessed using the MLP toolbox implemented in Matlab.Material and methodsA total of 20 participants with normal hearing sensitivity were selected for the study. The test–retest reliability of psychoacoustic measures was studied in terms of frequency difference limen, intensity difference limen, duration discrimination thresholds, gap detection thresholds, and modulation detection thresholds (4 Hz and 128 Hz). To check test–retest reliability all measures were assessed twice within a span of one day.ResultsThe results showed no significant difference in the various psychoacoustic measures obtained across the two sessions. The reliability of each measure was tested using the intraclass correlation coefficient (ICC).The results indicated that the test-retest reliability of various psychoacoustic measures assessed using the MLP toolbox was fair to good.ConclusionsIt can be concluded that MLP is a reliable tool to assess various psychoacoustic abilities.

An Analysis of Individual Differences in Recognizing Monosyllabic Words Under the Speech Intelligibility Index Framework.

Individual differences in the recognition of monosyllabic words, either in isolation (NU6 test) or in sentence context (SPIN test), were investigated under the theoretical framework of the speech intelligibility index (SII). An adaptive psychophysical procedure, namely the quick-band-importance-function procedure, was developed to enable the fitting of the SII model to individual listeners. Using this procedure, the band importance function (i.e., the relative weights of speech information across the spectrum) and the link function relating the SII to recognition scores can be simultaneously estimated while requiring only 200 to 300 trials of testing. Octave-frequency band importance functions and link functions were estimated separately for NU6 and SPIN materials from 30 normal-hearing listeners who were naïve to speech recognition experiments. For each type of speech material, considerable individual differences in the spectral weights were observed in some but not all frequency regions. At frequencies where the greatest intersubject variability was found, the spectral weights were correlated between the two speech materials, suggesting that the variability in spectral weights reflected listener-originated factors.

Robot-assisted assessment of wrist proprioception: does wrist proprioceptive acuity follow Weber's law?

Proprioception is essential for planning and controlling limb posture and movement. In our recent work, we introduced a standardized robot-aided method for measuring proprioceptive discrimination thresholds at the wrist to obtain reliable and accurate measures of proprioceptive acuity. Weber's law defines discrimination thresholds as a constant ratio between the just noticeable difference and the reference or standard stimulus. Reporting Weber's fractions thus provides the possibility of comparing results with the reports of others collected worldwide. This work aims to determine that Weber's Law holds for proprioceptive discrimination thresholds and to provide Weber's fraction for wrist joint proprioception. To this end, eight healthy subjects experienced two passive wrist movements of different amplitude and verbally indicated which was larger. An adaptive psychophysical procedure established the amplitude of the largest stimulus according to participants' responses. This comparison stimulus was then compared to a standard stimulus amplitude of 10°, 20°, 30° or 40°. The discrimination thresholds for each standard stimulus were established at the 75% correct response level. The obtained thresholds followed Weber's Law indicating that larger amplitudes were associated with higher discrimination thresholds. Based on a linear regression function the overall Weber's fraction, defined as the slope of the line, was computed to be 0.09. This result expands the present limited knowledge on wrist proprioception showing that its proprioceptive acuity follows Weber's law.

Deceived by stripes: conspicuous patterning on vital anterior body parts can redirect predatory strikes to expendable posterior organs.

Conspicuous coloration, which presumably makes prey more visible to predators, has intrigued researchers for long. Contrastingly coloured, conspicuous striped patterns are common among lizards and other animals, but their function is not well known. We propose and test a novel hypothesis, the ‘redirection hypothesis’, wherein longitudinal striped patterns, such as those found on the anterior body parts of most lacertilians, redirect attacks away from themselves during motion towards less vulnerable posterior parts, for example, the autotomous tail. In experiments employing human ‘predators’ attacking virtual prey on a touchscreen, we show that longitudinal striped patterns on the anterior half of prey decreased attacks to the anterior and increased attacks to the posterior. The position of stripes mattered—they worked best when they were at the anterior. By employing an adaptive psychophysical procedure, we show that prey with striped patterning are perceived to move slower, offering a mechanistic explanation for the redirective effect. In summary, our results suggest that the presence of stripes on the body (i.e. head and trunk) of lizards in combination with caudal autotomy can work as an effective anti-predator strategy during motion.

A late-emerging auditory deficit in autism.

Individuals with autism spectrum disorders (ASD) show enhanced perceptual and memory abilities in the domain of pitch, but also perceptual deficits in other auditory domains. The present study investigated their skills with respect to "echoic memory," a form of short-term sensory memory intimately tied to auditory perception, using a developmental perspective. We tested 23 high-functioning participants with ASD and 26 typically developing (TD) participants, distributed in two age groups (children vs. young adults; mean ages: ∼11 and ∼21 years). By means of an adaptive psychophysical procedure, we measured the longest period for which periodic (i.e., repeated) noise could be reliably discriminated from nonperiodic (i.e., plain random) noise. On each experimental trial, a single noise sample was presented to the participant, who had to classify this sound as periodic or nonperiodic. The TD adults performed, on average, much better than the other three groups, who performed similarly overall. As a function of practice, the measured thresholds improved for the TD participants, but did not change for the ASD participants. Thresholds were not correlated to performance in a test assessing verbal memory. The variance of the participants' response biases was larger among the ASD participants than among the TD participants. The results mainly suggest that echoic memory takes a long time to fully develop in TD humans, and that this development stops prematurely in persons with ASD.

An adaptive clinical test of temporal resolution: Within-channel and across-channel gap detection

Objective: Several methods exist to measure temporal resolution in a clinical setting. The Adaptive Tests of Temporal Resolution (ATTR©) are unique in that they incorporate an adaptive psychophysical procedure to present stimuli via computer sound card. The purpose of this study was to determine if ATTR gap detection thresholds (GDTs) were stable across presentation levels (80 dB SPL, listener-selected level) and sound cards (high-end, inexpensive). Design: GDTs were measured using three conditions of the ATTR: broad-band noise within-channel (BBN-WC), narrowband noise within-channel (NBN-WC), and narrowband noise across-channel (NBN-AC). Analysis of the acoustical properties of ATTR stimuli was made by measuring the electrical signals produced by each sound card. Study Sample: Participants were 30 young adults with normal hearing. Results: The ATTR GDTs did not differ between presentation levels for all three stimulus conditions. Also, neither ATTR stimuli nor ATTR GDTs differed between sound cards for all conditions. Conclusions: The ATTR may be used in a clinical setting with a relatively inexpensive sound card and listener-selected levels. Normative performance values for each ATTR condition are provided.SumarioObjetivo: Existen varios métodos en la clínica para medir la resolución temporal. La prueba adaptativa para la resolución temporal (ATTR@) es u´nica en el sentido en que incorpora un procedimiento psico-físico para presentar estímulos por medio de una tarjeta de sonidos de una computadora. El propósito de este estudio fue determinar si los umbrales de detección de brechas (GDT) de la ATTR eran estables en diferentes niveles de presentación (80 dB SPL, nivel seleccionado por el oyente) y con diferentes tarjetas de sonido (hig-end, barata). Diseño: Los GDT fueron medidos en tres condiciones de ATTR: banda ancha, ruido en el canal (BBN-WC), ruido de banda angosta en el canal (NBN-WC) y ruido de banda angosta a través del canal (NBN-AC). El análisis de las propiedades acústicas de los estímulos de ATTR fue realizado midiendo las señales eléctricas producidas por cada tarjeta de sonido. Muestra: Los participantes fueron 30 adultos jóvenes con audición normal. Resultados: Los GDT ATTR no difirieron en los niveles de presentación en las tres condiciones de estímulo. Además, ni los estímulos de ATTR ni los GDT ATTR difirieron en con las diferentes tarjetas de sonido en todas las condiciones. Conclusiones: Los ATTR pueden ser utilizados en condiciones clínicas con una tarjeta de sonido relativamente barata y a niveles seleccionados por el oyente. Se proporcionan los valores normativos de desempeño para cada condición de ATTR.

Overshoot using very short signal delays

The detectability of a 10-ms tone masked by a 400-ms wideband noise was measured as a function of the delay in the onset of the tone compared to the onset of the noise burst. Unlike most studies like this on auditory overshoot, special attention was given to signal delays between 0 and 45 ms. Nine well-practiced subjects were tested using an adaptive psychophysical procedure in which the level of the masking noise was adjusted to estimate 79% correct detections. Tones of both 3.0 and 4.0 kHz, at different levels, were used as signals. For the subjects showing overshoot, detectability remained approximately constant for at least 20-30 ms of signal delay, and then detectability began to improve gradually toward its maximum at about 150-200 ms. That is, there was a "hesitation" prior to detectability beginning to improve, and the duration of this hesitation was similar to that seen in physiological measurements of the medial olivocochlear (MOC) system. This result provides further support for the hypothesis that the MOC efferent system makes a major contribution to overshoot in simultaneous masking.

Interaction between gaze and visual and proprioceptive position judgements

There is considerable evidence that targets for action are represented in a dynamic gaze-centered frame of reference, such that each gaze shift requires an internal updating of the target. Here, we investigated the effect of eye movements on the spatial representation of targets used for position judgements. Participants had their hand passively placed to a location, and then judged whether this location was left or right of a remembered visual or remembered proprioceptive target, while gaze direction was varied. Estimates of position of the remembered targets relative to the unseen position of the hand were assessed with an adaptive psychophysical procedure. These positional judgements significantly varied relative to gaze for both remembered visual and remembered proprioceptive targets. Our results suggest that relative target positions may also be represented in eye-centered coordinates. This implies similar spatial reference frames for action control and space perception when positions are coded relative to the hand.

Early non-visual experience influences proprioceptive-spatial discrimination acuity in adulthood

The present study tested whether non-visual spatial experience affects later acuity of space perception. Congenitally blind adults who differed in the age acquired spatial knowledge via an orientation and mobility (O&M) training and matched sighted controls performed passive arm movements and judged the direction of the sensed movement. Proprioceptive-spatial discrimination acuity was assessed by an adaptive psychophysical procedure in two spatial coding conditions. In the egocentric coding condition, participants judged whether the hand trajectory felt left- or right-tilted in reference to a straight trajectory aligned to the transverse horizontal plane of the body midline axis. In the allocentric coding condition, they indicated whether the hand trajectory felt acute- or obtuse-angled in reference to a right angle. Proprioceptive-spatial acuity of congenitally blind participants significantly covaried with the age they attended an O&M training. The earlier the congenitally blind participants started the O&M training the more accurate was their space perception. Congenitally blind participants who underwent an O&M training after the age of 12 years showed poorer acuity than sighted controls. Congenitally blind participants with an earlier O&M training, however, approached the performance level of the sighted controls. The observed improvement in spatial acuity was more pronounced when judgements were given on the basis of an allocentric than an egocentric frame of reference. These findings suggest that proprioceptive-spatial acuity in adulthood depends on non-visual spatial experience during early development.

Cortical evoked response to gaps in noise: within-channel and across-channel conditions.

The objective of this study was to describe the cortical evoked response to silent gaps in a group of young adults with normal hearing using stimulus conditions identical to those used in psychophysical studies of gap detection. Specifically, we sought to examine the P1-N1-P2 auditory evoked response to the onsets of stimuli (markers) defining a silent gap for within-channel (spectrally identical markers) and across-channel (spectrally different markers) conditions using four perceptually-equated gap durations. It was hypothesized that (1) P1, N1, and P2 would be present and consistent for 1st marker (before the gap) onsets; (2) for within-channel markers, P1, N1, and P2 would be present for 2nd marker (after the gap) onsets only when the gap was of a duration equal to or larger than the behaviorally measured gap detection threshold; and (3) for the across-channel conditions, P1, N1, and P2 would be present for 2nd marker onsets regardless of gap duration. This is expected due to the additional cue of frequency change following the gap. Twelve young adults (mean age 26 years) with normal hearing participated. Within-channel and across-channel gap detection thresholds were determined using an adaptive psychophysical procedure. Next, cortical auditory evoked potentials (P1-N1-P2) were recorded with a 32-channel Neuroscan electroencephalogram system using within-channel and across-channel markers identical to those used for the psychophysical task and four perceptually weighted gap durations: (1) individual listener's gap detection threshold; (2) above gap detection threshold; (3) below gap detection threshold; and (4) a 1-ms gap identical to the gap in the standard interval of the psychophysical task. P1-N1-P2 peak latencies and amplitudes were analyzed using repeated-measures analyses of variance. A temporal-spatial principal component analysis was also conducted. The latency of P2 and the amplitude of P1, N1, and P2 were significantly affected by the acoustic characteristics of the 2nd marker as well as the duration of the gap. Larger amplitudes and shorter latencies were generally found for the conditions in which the acoustic cues were most salient (e.g., across-channel markers, 1st markers, large gap durations). Interestingly, the temporal-spatial principal component analysis revealed activity elicited by gap durations equal to gap detection threshold in the latency regions of 167 and 183 ms for temporal-parietal and right-frontal spatial locations. The cortical response to a silent gap is unique to specific marker characteristics and gap durations among young adults with normal hearing. Specifically, when the onset of the 2nd marker is perceptually salient, the amplitude of the P1-N1-P2 response is relatively larger and the P2 latency is relatively shorter than for nonsalient 2nd marker onsets, providing noninvasive, nonbehavioral indicators of the neural coding of this important temporal cue in the thalamic-cortical region of the central auditory system. Gap duration appears to be most clearly indicated by P1 and T-complex amplitude.

Objective and subjective measures of vergence step responses

Dichoptic nonius lines are used for subjectively (psychophysically) measuring vergence states, but they have been questioned as valid indicators of vergence eye position. In a mirror-stereoscope, we presented convergent and divergent step-stimuli and estimated the vergence response with nonius lines flashed at fixed delays after the disparity step stimulus. For each delay, an adaptive psychophysical procedure was run to determine the physical nonius offset required for subjective alignment; these vergence states were compared with objective eye movement recordings. Between both measures of initial vergence, we calculated the maximal cross-correlation coefficient: the median in our sample was about 0.9 for convergence and divergence, suggesting a good agreement. Relative to the objective measures, the subjective method revealed a smaller vergence velocity and a larger vergence response in the final phase of the response, but both measures were well correlated. The dynamic nonius test is therefore considered to be useful to relatively evaluate a subject’s ability in disparity vergence.

Effect of adaptive psychophysical procedure on loudness matches

Large variability in equal-loudness matches has been observed across studies. The purpose of the present study was to gain insight into the extent to which this variability results from differences in psychophysical procedures and/or differences among listeners. Four adaptive two-interval, two-alternatives-forced-choice procedures were used to obtain equal-loudness matches between 5- and 200-ms 1-kHz tones as a function of level for each of six normal listeners. The procedures differed primarily in the sequence in which the stimuli were presented. The variations tested were the ordering of stimuli by amplitude across blocks of trials (both increasing and decreasing amplitudes), randomizing the order across those blocks, and randomizing the order within blocks. The random-within-block procedure, which sought to randomize any intertrial information, yielded a significantly greater amount of temporal integration than the other three procedures. The results show significant differences in temporal integration measurements at moderate levels for the same listeners across different procedures. Therefore, although there are individual differences among listeners in the amount of temporal integration measured across paradigms, the choice of paradigm also affects the amount of temporal integration measured at moderate levels.

Genetic Algorithms for Adaptive Psychophysical Procedures: Recipient-Directed Design of Speech-Processor MAPs

The goal of the research is to evaluate the application of genetic algorithms (GAs) in listener-directed optimization of audio-processing designs. We hypothesize that cochlear-implant recipients can use a GA-guided adaptive psychophysical search procedure to select useful designs from among a large number of speech processor MAPS. An adaptive psychophysical procedure was developed in which a listener's preferred four out of eight speech processor MAPs were updated according to a genetic algorithm. Experiments involving cochlear-implant recipients were conducted to characterize both the convergence behavior of the adaptive procedure as well as properties of the MAPs optimized by the recipient. Results from five cochlear-implant recipients indicate that the adaptive procedure converges to useful speech processor MAPs within twenty iterations. The results suggest a means whereby a potentially large number of audio-processing designs can be searched efficiently by a human listener without requiring excessive amounts of feedback or prior knowledge about the listener's preferences. In the case of cochlear-implant recipients, it may be possible to use this procedure as an aid to the clinician in the fitting of a speech processor MAP.

Vibration perception thresholds of human maxillary and mandibular central incisors

Tactile information from dental mechanoreceptors contributes to the perception of food bolus textures and the control of mastication. While numerous studies have measured the light-touch sensory thresholds of teeth, little information is available about the vibrotactile perception thresholds of teeth. This study uses an adaptive psychophysical procedure to determine thresholds of vibratory stimulation of maxillary and mandibular central incisors in 16 healthy human subjects. An electromechanical vibrator delivered labiolingual forces perpendicular to the long axis of the maxillary and mandibular incisors at 10 stimulation frequencies between 40 and 315 Hz. The median thresholds ranged between 44 and 104 mN. A linear regression analysis revealed a significant increase in the vibrotactile thresholds with increasing frequencies for stimulation of the maxillary and mandibular incisors. No significant differences were found between regression slopes of the thresholds of the maxillary and mandibular incisors. These results indicated that maxillary and mandibular incisors should be able to discriminate effectively among a variety of textures based on their ability to encode a wide range of vibration frequencies.

Impaired short temporal interval discrimination in a dyslexic adult

The ability to discriminate short temporal intervals was examined in a dyslexic adult (E.C.) and six matched controls. Listeners had to decide whether the second interval was shorter or longer than a standard (target) interval. Each interval was defined as the silent duration between two successive brief tones. Eight target intervals were used, ranging from 100 to 1,200 ms in duration. At each target interval, the differential threshold (DL) for duration was assessed, with the use of an adaptive psychophysical procedure. The results show that E.C.'s differential threshold values were much larger than those of controls. Moreover, the slope estimates covering the duration range from 100 to 800 ms indicated that in comparison to controls, E.C.'s differential threshold increased dramatically as the target duration increased. Thus her timing impairment becomes more pronounced with increasing duration. This timing deficit is consistent with other studies that have found temporal processing deficits associated with dyslexia.