Reference Stimulus Research Articles

Matching large color differences with achromatic and chromatic surrounds

AbstractA color‐difference‐matching experiment was carried out using a computer‐interfaced video‐display system. Two reference color stimuli (i) and (j), and one test stimulus (i,j) surrounded by a large achromatic or chromatic stimulus were presented on the video screen. An observer was asked to adjust the test stimulus until he perceived it to have a color precisely “half way” between the colors of the given reference stimuli. A satisfactory half‐way color was the one that produced perceptually equal color differences between (i) and (i,j) and (j) and (i,j) and simultaneously made these color differences as small as possible. Although the given color difference between the test stimuli (i) and (j) was generally quite large (100–200 just‐perceptible color‐difference steps) with the achromatic surround condition, the color‐difference matching required to obtain the desired half‐way color did not present any serious difficulties to the observer. The uncertainty of the chromaticity point of the half‐way color was established by an ellipse of small to moderate size surrounding the mean chromaticity setting. The orientation and shape of the uncertainty ellipse was comparable with the orientation and shape of uncertainty ellipses obtained by other investigators studying color‐difference matching involving much smaller color differences. The unexpected and noteworthy result of the present study lies in the location of the chromaticity point of (i,j) relative to those of (i) and (j) as a function of surround color. The location of (i,j) depends on the saturation of the surround stimulus but not its hue. Some speculative explanations of the observed results are offered.

Continuous measurement of visible persistence.

In the synchrony judgment paradigm, observers judge whether a click precedes or follows the onset of a light flash and, on other trials, whether or not a click precedes light termination. The interclick interval defines the duration of visible persistence. An elaboration of this method consists of two phases: In Phase 1, the luminance of a reference stimulus is psychophysically matched to the peak brightness of the test flash. Five luminance values between .1 and 1.0 of the reference stimulus are used subsequently. In Phase 2, a random one of the five reference stimuli, a test flash, and a click are presented; the observer judges whether the click occurred before or after the brightness of test flash reached the reference value (on onset trials) or decayed below it (on termination trials). This method was validated on 3 subjects with test stimuli whose luminance rises and decays slowly in time, and then was used to trace out the precise subjective rise and decay (temporal brightness response function) of brief flashes.

The development of orientation categories between 2 and 4 months of age

Recent research has indicated that infants are capable of responding to stimuli in a manner indicating that they categorize them. Infant perception of orientation was examined within a framework of categorization. In one experiment, it was shown that 4-month-old infants generalized habituation from one range of oblique grating stimuli to another, consistent with the interpretation that any two oblique stimuli were perceived as more similar than a vertical and an oblique. Fourmonth-old infants' generalization was not due to a simple inability to discriminate between obliques (Experiment 2) so the results of Experiment 1 reflect in large part true categorization behavior and not categorical perception. Results for 2- and 3-month old infants suggest that “vertical” serves as a reference stimulus in infant orientation perception such that gross distinctions between vertical and nonvertical precede the development of the “oblique” category. The category boundary between oblique and vertical did not successfully predict better between-than within-category discrimination in 4-month-old infants (Experiment 3) under the conditions of these experiments.

How loudly should you hear your colleagues and yourself

A choir singer needs to hear both the sound of his/her own voice and the sound of the other choir members. If either of these signals becomes too loud, problems can be assumed to arise. The present study investigates the importance of the amplitude ratio between the sound of one's own voice and the sound of an external reference signal. Nine male choir singers were asked to sing in unison with synthetic reference vowel stimuli presented over earphones. In the earphones they also heard the sound of their own voice as picked up by a microphone in front of the mouth. The SPL of the reference stimuli was varied over a range of 40 dB, while the subjects were asked always to sing at a constant SPL, as indicated by a level meter. The fundamental frequency agreement between the reference and the subjects' responses was analyzed. The fundamental frequency of the responses depended strongly on the SPL of the reference in the case of the vowel /u/, presumably because of a pitch-amplitude dependence, which, however, was compensated for in the analysis. It was found that the fundamental frequency agreement between the reference vowels and the corrected responses was approximately constant over a dynamic range of 20 dB of the reference vowels. Outside this range, choir singers tended to fail in matching the pitch of the external reference.

How does vowel duration affect loudness in a CV syllable?

The objective of our current experiments is to examine the effect of duration on loudness in CV syllables. A natural [ta] was manipulated with the aid of a computer so as to generate a reference stimulus of 250 ms at 70 dB SPL and a series of test stimuli with duration of 75, 100, 150, 200, and 250 ms. The stimulus interval was 200 ms in experiment I, and 600 ms in experiment II. A computer-assisted method of adjustment was set up. The measured level difference in dB between the reference stimulus and the adjusted test stimulus is less than 2 dB for the shortest duration, and is equal to 0.2 dB for the longest one. In experiment III, the Up-Down-Transformed-Response procedure was used with the same stimuli as in experiment II. Resulting level differences values, when plotted, had the same loudness contour as in experiment I and II, but were slightly higher.

Sensitivity of Seated Subjects to Low Frequency Random Vibrations in the Vertical Direction. Subjective Approach Using Vibrations Representative of Earthmoving Machines

A study was conducted to compare various methods for evaluating complex vibrations. The two methods recommended by the Standard ISO 2631 were tested. A subjective equalization technique was used in which 10 seated subjects were asked to adjust the intensity of a test stimulus until they perceived a whole body sensation equivalent to a reference stimulus. The vibration stimuli were low frequency motions along the vertical axis and they were representative of earthmoving machines. They were compared to each other and to sinusoidal and third octave band random vibrations centred at the same frequencies. The results obtained indicate that the overall frequency weighting methods are the most appropriate for the evaluation of complex vibrations. The vertical weighting curve recommended by the Standard ISO 2631 produces suitable results.

Perceived rate of randomly modulated sounds

The common measures used in evaluating the magnitude of a noise (Lx, Leq, and etc.) correspond to first- and second-order statistics of the distribution of sound levels. There are, however, perceived differences between sounds that have the same values of these statistics. It is therefore necessary to consider the spectral properties of the waveform envelope which correspond to higher-order statistics. In the present experiments the subject compares a test stimulus and a reference stimulus and selects the one which appears to be fluctuating more rapidly. The reference stimulus is a noise whose waveform envelope is a noise with a low-pass cutoff which varies from 0.125 to 8 Hz. The point of subjective equality is determined by adjusting the modulation frequency of the test stimulus, a sinusoidally modulated noise, in an adaptive procedure. The results indicate that when the median frequency of the spectrum of the envelope is above 1 Hz, it is a reasonably good predictor of the subjective rate, when the median is below 1 Hz the mode is a better predictor. [Work supported by NINCDS.]

Conformity And Judgments Of Fashionability

The effects of reference group influences and stimulus ambiguity on conformity in judgments of the fashionability of clothing were investigated using an established conformity paradigm. In a laboratory experiment, 160 female subjects made a reassessment of their original opin ions of the fashionability of six women's suits after being exposed to opinions attributed to one of four reference groups: peers, fashion experts, housewives, or career women (a control group received no group influence manipulation). In addition, half the subjects made judg ments of the present fashionability and half made judgments of the fashionability two years from now. Greater conformity resulted for the more ambiguous judgments of future fash ionability than to judgments of present fashionability. Individuals also conformed more when the opinion was attributed to fashion experts than when the opinion was attributed to the other reference groups. Results are discussed in terms of social influence processes underlying conformity, and implications for fashion research are drawn.

Spectral luminous efficiency functions for a ten-degree field in the mesopic range.

Mesopic photometry is one of the current problems of the CIE TC-1.4. The luminous efficiency function for mesopic vision has not been established yet, whereas the functions V(λ) for photopic vision and V'(λ) for scotopic vision have been already standardized. In the present study, we measured the spectral luminous efficiency functions in the mesopic range extensively to offer basic data for making photometry more visually meaningful. A direct brightness matching method of 10° field was employed. White light was used as a reference stimulus, and its retinal illuminance was varied from 0.01 to 100 photopic trolands in 0.5 log unit steps to cover the mesopic range. Spectral luminous efficiency function from 400 to 700 nm in 10 nm steps was measured for each retinal illuminance level. Data of seven subjects (19-23 yr old) were collected. It was shown that the function obtained changed gradually from the photopic function to the scotopic one as retinal illuminance decreased. The average and individual variation of seven subjects’ data were presented as basic data of luminous efficiency for mesopic vision. The change of the function due to the different contributions of photopic and scotopic functions was discussed according to the Ikeda-Shimozono’s formula.

On the just‐detectable modulation of the spectral envelope on a log‐∫ scale

The interesting aspect of this study is the use of a spectral ripple on a log‐f scale. The computer‐generated stimuli consist, basically, of 160 frequency components added in random phase, separated by 1/40‐octave intervals and covering the range of 250 to 4000 Hz. In a forced choice procedure, the reference stimulus had a flat spectral envelope (level of each component Lf = const.), whereas the spectral envelope of the target stimulus was slightly modulated according to Lf = const. + d sin (2π n log f/log 2). The parameter n indicates the number of ripples per octave, whereas d was treated as the dependent variable in an adaptive 2‐AFC measuring procedure. It is found that the just‐detectible peak‐to‐valley ratio shows a distinct minimum for about two ripples per octave. This result agrees well with the concept of an auditory filter shape with a suppression area which is located about a factor 1.2 above the filter's nominal frequency.

Speech referenced equal loudness contours for pure tones

Equal loudness contours for pure tones with speech as the reference stimulus were established through an alternate monaural loudness balance procedure. Untrained subjects compared the loudness of a nonmeaningful sentence presented at 10, 30, 50, 70, and 85 dB sensation levels (re: speech detection threshold) to the loudness of six pure tones in the octave test frequency range, 250–8000 Hz. The speech levels and the pure tone frequencies were randomized during the presentation. The results suggest: (1) a similar shape for the contours plotted in terms of sensation level and hearing threshold level in contrast to the contours based on sound pressure level (SPL), (2) a different shape for SPL based contours when compared to the classical pure tone equal loudness contours, and (3) a spread of loudness matches which varied with pure tone frequency and speech presentation level. A discussion of the results will be presented.

“Temporal masking” in discrimination of tone glides

Difference limens for tone-glide stimuli are reported to be greater when the glide precedes a contiguous 200-ms fixed-frequency segment than when the glide follows a contiguous fixed-frequency segment [M. J. Collins and H. Stromberg, J. Acoust. Soc. Am. 66, Suppl. 1, S9 (1979)]. The present study was carried out to test the hypothesis that the effect was due, in part, to “temporal masking” of the tone glide by the fixed-frequency segment. Six normal hearing subjects served as listeners. Reference stimuli consisted of 30-ms glide segments, preceded or followed by fixed-frequency (2200 Hz) segments of varied duration. Endpoint frequencies of the reference glide segments were 1680, 2200, and 2710 Hz for both glide-preceding and glide-following conditions. Results indicated that, in general, a greater amount of “masking” was imposed by fixed-frequency segments which preceded glides than by fixed-frequency segments which followed glides. This was particularly evident for the conditions which involved discrimination between no glide and some glide (2200-Hz endpoint frequency): essentially no “forward” masking was observed with significant “backward” masking for the comparable glide-preceding condition. [Work supported by NIH.]

Discrimination of time‐varying signals by hearing‐impaired listeners

For normal hearers, difference limens for tonal glides are larger for glides which precede fixed‐frequency segments than for glides which follow the fixed‐frequency segments [Collins and Stromberg, J. Acoust. Soc. Am. Suppl. 1 66, S9(A) (1979)]. In the present study similar measurements were made on each ear of two hearing‐impaired subjects. The reference stimuli had 200‐ms fixed‐frequency segments of 2200 Hz and were preceded or followed by 30‐ms glides with endpoints of 2710, 2200, 1690, or 1180 Hz. Difference limens were determined, using an adaptive procedure, on each side of each referent. The hearing‐impaired subjects showed larger than normal difference limens, on the average. However, for frequency ranges where hearing loss was less severe, the results approximated normal. The deviations from normal were greater for glides which followed fixed‐frequency segments than for those which preceded. Thus, the consistent difference between difference limens for preceding versus following glides for normal hearers was reduced in some instances and even reversed in others for the hearing‐impaired listeners. [Work supported by NINCDS, Grant No. IF32 NS 06053.]

Acquiring Relative Pitch Perception as a Function of Age

The purpose of this study was to examine the ability to learn relative pitch-perception, and how it is affected by age, frequency, and ear. Thirty-four musically naive subjects were assigned to four age groups and taught individually, over a period of five daily sessions, to adjust the frequency of a variable stimulus to be twice the frequency of (or an octave higher than) a specified reference stimulus. Three-octave intervals were learned in this manner with either the left or right ear. Results indicated no age or ear difference in amount of accuracy attained. The octave interval 1000–2000 Hz appeared significantly more difficult to estimate accurately than the octave intervals 400–800 Hz or 1500–3000 Hz, however. The youngest age group learned the task with maximum accuracy more quickly than the older age groups. There was, furthermore, a significant ear difference in how quickly the task was learned. This difference, however, was frequency-dependent.

Use of the ’’acoustic menu’’ in assessing human response to audible (corona) noise from electric transmission lines

A behavioral preference procedure, the ’’acoustic menu,’’ was used to assess human aversion to the sounds from two samples of transmission line audible noise and from samples of other environmental noises. The audible (corona) noise produced by extra-high voltage (EHV), overhead transmission lines was tape-recorded during moist weather. Reproduced samples of corona noise, other common environmental noises, and artificial reference stimuli were compared in two experiments. The two corona noise samples were found to be equally preferred to: (1) a 1000 Hz octave band of noise about 11 dB SPL higher than the corona noises and (2) a collection of other environmental noises about 8 dB SPL higher than the corona noises. The corona noise samples were more aversive than the ambient sounds (including rainfall) occurring near rural transmission lines and were roughly equivalent in aversiveness to the noise from a room air conditioner (indoor recording). Knowledge of the source of the corona noise (from photographs and a brief description) did not affect its aversiveness. Of the simple frequency-weighting scales, the A-weighted sound level reduced the difference between the two corona noise samples and the set of other environmental sounds from about 8 dB SPL to about 3 dB. The D-weighted sound level further reduced this discrepancy to about 2 dB. These results were obtained with only two samples of corona noise; other samples may give different results.

Evaluation of color discrimination in the white region

Reference and test stimuli were produced on two separate color television screens to evaluate the color discrimination ability of the human eye for near-white colors. Each test stimulus had a luminance approximately equal to that of the reference, but was slightly different in chromaticity, e.g., [deltax] less than 0.01, [deltay] less than 0.01. The evaluation involved 20 persons observing 26 sets of color stimuli of 16-cd/m2 luminance, and 21 persons observing sets of color stimuli of 253 cd/m2. Observers were requested to categorize the color differences they perceived on a six-level rating scale. The results indicate that the differential thresholds for color difference of near-whites are between 4 and 8 CD (Color Difference), except in the bluish region.

Beitrag einzelner parameter zum wahrnehumungsgemäßen unterschied von zusammengesetzten reizen bei der honigbiene

The perceptual difference between stimuli can be regarded as distance within the perceptual space of the bee. The author used this assumption to determine the specific distance function, on the basis of which the differences in the individual perceptual parameters constituted the perceptual difference between the complex stimulus and the reference stimulus. The perceptual differences can be deduced only indirectly from the choice frequency. Consequently, it was necessary to establish a "calibration curve", to deduce quantitatively the perceptual difference from the choice frequency. The resulting hyperbolic curves for the parameters "brightness" and "size" were almost identical (Fig. 2). The perceptual difference between the complex stimulus and the reference stimulus is greater than one would expect in an Euclidean space. Rather it is the sum of the distances along the perceptual parameters which compose the complex stimulus (Fig. 3). Thus, the bee determines the perceived difference of composite stimuli which affect the perceptual parameters "brightness" and "size" in terms of the city-blockmetric.

The rate of “mental rotation” of images: A test of a holistic analogue hypothesis

This paper discusses the analogue-propositional distinction and argues that, given an appropriate understanding of this issue, the question of whether a particular cognitive function is analogue or not is an empirical one. As an example of how the question can be empirically investigated, the proposed analogue operation for mental rotation of images is considered. It is argued that the view that images are rotated in a holistic analogue manner should predict that rotation rate is independent of such factors as the conceptual complexity of the stimulus or of the comparison task. Two experiments are described that investigated the effects of several stimulus and task variables on the apparent rate of “mental rotation” of images in a Shepard-type task. Instead of comparing a stimulus and misoriented probe figure to determine whether they are identical (except for orientation) or mirror images, as was the case in most of previous studies, the present experiments required subjects to judge whether the misoriented probe was a subfigure of the target stimulus. The results showed that the “rotation rate” (i.e., the slope of the RT vs. angle of misorientation function) was influenced by practice, stimulus attributes, and the nature of the comparison task. In particular, when the probe was a “good” subfigure of the reference stimulus, apparent rotation rate was greater. These results are interpreted as indicating that the linear RT vs. angle relation is not due to a holistic analogue rotation of images, as had been supposed, but arises from a more articulated and piecemeal process in which analysis of the stimulus figure interacts with the comparison task.

Human response to audible noise from high‐voltage transmission lines

The aversiveness of audible (corona) noise produced by extra‐high voltage (EHV) overhead transmission lines during moist weather was assessed. Samples of corona noise from two lines, other common environmental noises, and artifical reference stimuli were compared using a behavioral preference procedure. Corona noise samples were found to be equally preferred to (1) a 1000‐Hz octave band of white noise approximately 12 dB SPL higher than the corona noises and (2) a collection of other environmental noises approximately 9 dB SPL higher than the corona noises. Corona noise was significantly less preferred than the ambient noises occurring near the transmission lines. One sample of corona noise was comparable in aversiveness to a sample of room air conditioner noise; the other sample of corona noise was somewhat more aversive. While all of the commonly used frequency weighting scales correlated strongly with preference, D‐weighted sound level provided the highest correlation with the preference data and the smallest standard error bands. [Sponsored by the Department of Energy.]

Effects of fixed versus variable reference frequencies on psychophysical judgments of vibration.

Equal magnitude contours for vibration were obtained by two methods from ten seated subjects exposed to sinusoidal vibrations in three axes. In the traditional “fixed reference frequency” method, subjects were asked to adjust the amplitude of vibration in order to match for equal vibratory magnitude of a variable stimulus (of from 1 to 30 Hz) to a fixed reference vibration stimulus. The reference stimulus corresponded to the ISO 1–4 min “reduced comfort boundary” level; i.e., 6 Hz at 0.9 m/s2 (rms acceleration) for vertical (±gz) axis and 1 Hz at 0.62 m/s2 rms acceleration for the lateral (±gy) and longitudinal (±gx) axes. In the modified “progressive matching” method, subjects were exposed initially to the same reference stimulus and matched the adjoining stimulus vibratory frequency magnitude to it. Then, however, the newly matched vibration frequency was used as the next reference stimulus, the subjects matched the adjoining frequency magnitude to this “new” reference stimulus, etc. over the same range of frequencies (from 1 to 30 Hz). The advantages and shortcomings of the two methods are discussed.