A comparison of sniff bottle staircase and olfactometer-based threshold tests

Olfactometers have been gaining popularity as research tools, but they have yet to replace established testing procedures in a variety of laboratory and clinical settings, including absolute threshold tests. In this research, we designed and operated a simple olfactometer with which to assess threshold. To do this, we used a method-of-adjustment test that was compared to the three-alternative forced choice ascending sniff bottle staircase method, which is currently a standard threshold test procedure. We found that the olfactometer threshold test correlated highly with the staircase method, and that it possessed suitable test–retest reliability. The advantages of the olfactometer threshold test include faster test time and reduced cleaning and reassembly demands. Future use of the olfactometer in olfactory identification and/or detection thresholds amongst odors is also outlined.     

A comparison of three adaptive psychophysical procedures using inexperienced listeners

Thresholds for a masked 1-kHz tone were obtained in single sessions from 60 inexperienced listeners. A two-alternative forced-choice procedure was used in conjunction with one of three adaptive psychophysical techniques. These techniques comprised two staircase techniques targeting either 70.7% or 79.4% correct detection (Staircase-71 and Staircase-79), and parameter estimation by sequential testing (PEST), targeting 80% correct detection. Listeners were provided with a rationale for maintaining concentration at weak signal levels. Similar threshold values were obtained from the Staircase-79 and PEST groups in equal numbers of trials. The degree of oscillation in the level of the signal around the value finally chosen as the threshold was comparable for both staircase techniques. Subsequent fixed-level testing did not provide a true indication of the subjects' capabilities. The amount by which percent correct in fixed-level testing differed from expectations based on adaptive testing varied among the techniques. Additional thresholds were obtained in a second session from 30 of the original subjects. Thresholds with both staircase techniques improved by about 1 dB on retest, while thresholds with PEST were constant across sessions. The variability of the data compared well with that from studies involving experienced listeners.     

Operant methods for mouse psychoacoustics

Tone detection thresholds for a 10-kHz tone in NMRI mice were determined in psychoacoustic experiments using both a constant-stimuli procedure and a two-down/one-up adaptive-tracking procedure in the same subjects and applying identical threshold criteria (70.7% response probability). Constant-stimuli thresholds were on average 24 dB lower than adaptive-tracking thresholds, and there was a trend indicating that constant-stimuli thresholds were less variable than adaptive-tracking thresholds. Furthermore, in the constant-stimuli procedure the number of trials constituting the psychometric function could be reduced from 100 to 50 trials without a large loss of accuracy of threshold determination. In the constant-stimuli procedure, the threshold value was affected by the threshold criteria. The lowest and least variable constant-stimuli thresholds were obtained by applying signal detection theory and a criterion ofd′=1. Thus, the constant-stimuli procedure in combination with signal detection theory appears to be better suited than the adaptive-tracking procedure to determine auditory sensory thresholds.     

Animal psychophysics: improvements in the tracking method.

It is difficult to maintain stimulus control in animal psychophysical studies using the tracking method. Loss of stimulus control is characterized by wandering thresholds and responses in the absence of the stimulus. Rats were trained to make a variable number of licking responses to turn on an auditory stimulus. A response on a lever in the presence of the stimulus was reinforced with food. Two precedures were added to improve stimulus control. First, lever responses in the absence of the stimulus raised the intensity of the stimulus at the next presentation; second, rate of reinforcement in the threshold region was maintained at about the same level as that in the suprathreshold region by reducing the number of licking responses required to turn on the stimulus. Using these two procedures, stimulus control was improved and maintained and reliable auditory intensity thresholds were obtained.     

Temporal summation of pain from radiant stimulation

Latency thresholds of pricking pain, using radiant thermal stimulation, were obtained. Ten Ss were tested for 10 sessions, and, in each session, single latency determinations were made at each of 10 stimulus intensities. Each intensity was administered to a different spot along the volar surface of S’s nonpreferred forearm. Thus, 10 latency thresholds were obtained from each S at. each intensity and each spot. Initial skin temperature was controlled so that a threshold determination was made when skin temperature measured 33.5° ± 0.5° C. Analysis of variance of the log₁₀ t (seconds) values revealed a highly significant linearity of regression of log t on log intensity, thus confirming the hypothesized inverse and exponential relationship between latency and intensity. The parameters (slope and x-intercept) of the curve were discussed. The x-intercept may be interpreted as an index of an aversive threshold and could be used as a possible measure of the physiological component of pain.     

Orientation discrimination across the visual field: size estimates near contrast threshold

Performance in detection and discrimination tasks can often be made equal across the visual field through appropriate stimulus scaling. The parameter E2 is used to characterize the rate at which stimulus dimensions (e.g., size or contrast) must increase in order to achieve foveal levels of performance. We calculated both size and contrast E2 values for orientation discrimination using a spatial scaling procedure that involves measuring combination size and contrast thresholds for stimuli with constant size-to-contrast ratios. E2 values for size scaling were 5.77 degrees and 5.92 degrees. These values are three to four times larger than those recovered previously using similar stimuli at contrasts well above detection threshold (Sally & Gurnsey, 2003). E2 values for contrast scaling were 324.2 degrees and 44.3 degrees, indicating that for large stimuli little contrast scaling (.3% to 2.3% increase) was required in order to equate performance in the fovea and the largest eccentricity (10 degrees). A similar pattern of results was found using a spatial scaling method that involves measuring contrast thresholds for target identification as a function of size across eccentricities. We conclude that the size scaling for orientation discrimination at near-threshold stimulus contrasts is much larger than that required at suprathreshold contrasts. This may arise, at least in part, from contrast-dependent changes in mechanisms that subserve task performance.     

Natural sniffing gives optimum odour perception for humans

The characteristics of human sniffing episodes during odour perception have been described in an earlier paper, where it has been suggested that the techniques used by individuals may be close to those providing optimum perception. To investigate this suggestion, threshold and intensity tests with butanol, cyclohexanone, and pentyl acetate have been carried out on twenty-one subjects. Olfactory responses obtained by using natural sniffing techniques were compared with those where the number of sniffs, interval between sniffs, and size of sniffs were varied. The results indicate that it is very difficult to improve on the efficiency of sniffing techniques of individuals and that a single natural sniff provides as much information about the presence and intensity of an odour as do seven or more sniffs. A single natural sniff and the first sniff of a a natural sniffing episode were shown to have similar characteristics and most significantly both were unaffected by changes in the concentration and type of odour. Overall, the results indicate that humans achieve optimum odour perception during threshold and intensity measures with their natural multiple-sniff technique or with a single sniff. For the 'average' human this occurs with a sniff of inhalation rate 30 1 min-1, volume 200 cm3, and duration 0.4 s. The use of several sniffs in a sniffing episode appears to be a confirmatory action rather than a necessary one, except for the perception of odour mixtures where several sniffs are likely to be needed to aid discrimination of the components. Data from the present and earlier study provide the information necessary for the development of a standard olfactometer and standard procedures for measuring the olfactory responses of humans.     

Lingual vibrotactile threshold alterations in response to varying stimulation levels of intensity and duration.

Lingual vibrotactile thresholds were obtained at a frequency of 250 Hz by using an ascending-continuous series of stimulation during five sessions. Each of three adult male Ss attended a control session which included a prescribed period of constant tongue positioning, a pre-experimental session where the mean of six thresholds was obtained as a basis of further testing, and three experimental sessions. In the experimental sessions vibrotactile thresholds after exposure to vibratory stimulation of varying levels of intensity and duration were obtained. The findings of the control session reflected a slight pattern of decreased lingual sensitivity indicative of the influential factor of constant maintenance of tongue positioning. Results from the experimental sessions demonstrated shifts toward progressively decreased lingual sensitivity after exposure to vibratory signals of increased levels of intensity and duration. A recovery phase to near-normal sensitivity followed each stimulus presentation.     

Effects of auditory disruption of lingual tactile sensitivity in skilled and unskilled speaking conditions.

The purpose of this study was to investigate the effect of disruption of the auditory feedback channel on lingual vibrotactile thresholds obtained under skilled and unskilled speaking conditions. Each of 22 adults was asked to read an English (skilled) and French (unskilled) passage under conditions of normal and altered auditory feedback. Bilateral presentation of masking noise was utilized to disrupt auditory feedback. Before each of the experimental sessions and immediately following a reading, lingual vibrotactile thresholds were obtained. Analysis indicated that the mean differences in the pre- and postvibrotactile threshold measurements of the skilled auditory disrupted condition varied significantly from the mean differences in the pre- and postvibrotactile threshold measurements of the three other conditions. The role of feedback in the speech production of skilled and unskilled speakers is discussed.     

Behavioral limits of auditory temporal resolution in the rat: amplitude modulation and duration discrimination

Thresholds for detecting the presence of amplitude modulation in a noise carrier were determined for rats using conditioned avoidance procedures. There was a progressive increase in threshold with modulation rates between 5 Hz and 2 kHz. Further tests were conducted to determine difference thresholds for detecting an increase in modulation rate for standard rates of 10, 50, and 100 Hz. The size of the difference threshold increased progressively as the standard rate increased. In addition, thresholds for detecting an increase in the duration of a noise burst were determined for various standard durations. The difference thresholds were constant for values between 10 and 50 ms but increased progressively, with standard durations between 0.1 and 1.0 s.     

Detection by the guinea pig of acoustic stimulation and of electrical stimulation of the brain

A threshold procedure using operant behavioral techniques with positive reinforcement was developed after initial efforts with avoidance behavioral procedures proved unsatisfactory. In the first of three experiments the operant threshold procedure was tested by determining masked auditory thresholds for trains of clicks. In a second experiment, similar techniques were used to measure thresholds for electrical stimulation of the brain. The last experiment, again an auditory problem, involved a determination of the absolute thresholds for trains of short noise bursts as a function of the time between bursts. Middle ear malfunction proved to be a more severe problem than had been anticipated on the basis of reports in the literature. The threshold procedure, however, seems to be adequate for determination of absolute or masked thresholds with auditory or electrical stimuli.     

Tracking of nociceptive thresholds using adaptive psychophysical methods

Psychophysical thresholds reflect the state of the underlying nociceptive mechanisms. For example, noxious events can activate endogenous analgesic mechanisms that increase the nociceptive threshold. Therefore, tracking thresholds over time facilitates the investigation of the dynamics of these underlying mechanisms. Threshold tracking techniques should use efficient methods for stimulus selection and threshold estimation. This study compares, in simulation and in human psychophysical experiments, the performance of different combinations of adaptive stimulus selection procedures and threshold estimation methods. Monte Carlo simulations were first performed to compare the bias and precision of threshold estimates produced by three different stimulus selection procedures (simple staircase, random staircase, and minimum entropy procedure) and two estimation methods (logistic regression and Bayesian estimation). Logistic regression and Bayesian estimations resulted in similar precision only when the prior probability distributions (PDs) were chosen appropriately. The minimum entropy and simple staircase procedures achieved the highest precision, while the random staircase procedure was the least sensitive to different procedure-specific settings. Next, the simple staircase and random staircase procedures, in combination with logistic regression, were compared in a human subject study (n = 30). Electrocutaneous stimulation was used to track the nociceptive perception threshold before, during, and after a cold pressor task, which served as the conditioning stimulus. With both procedures, habituation was detected, as well as changes induced by the conditioning stimulus. However, the random staircase procedure achieved a higher precision. We recommend using the random staircase over the simple staircase procedure, in combination with logistic regression, for nonstationary threshold tracking experiments.     

Measuring threshold shifts for brain stimulation reward using the method of limits.

Thresholds determined from the frequency of pulses and the current for rewarding brain stimulation were obtained from rats with lateral hypothalamic electrodes. The threshold, defined as the frequency or current corresponding to one-half the maximum response rate, was interpolated from reward summation functions. Daily trials of both ascending and descending sequences of frequency and current yielded no significant difference between order of presentation. While there was more variability in the maximum response rates across the sessions, neither frequency- nor current-based threshold evaluations yielded significant rate effects. Our findings suggest that the threshold procedure is generally not influenced by the sequence of delivery of stimulus values and, thus, may be regarded as a reliable measure of the reinforcing properties of brain-stimulation reward.     

Frequency selectivity in the parakeet (Melopsittacus undulatus) studied with psychophysical tuning curves

Seven parakeets were trained to avoid shock during pure-tone stimulation. A modified method of limits was used to measure detection thresholds of the pure tones. The intensity of masker tones, at numerous frequencies, was varied in order to measure the masked threshold of a probe-tone signal set at a fixed frequency and intensity. Masking curves were obtained for three probe tones (.63, 1.6, and 2.5 kHz) at each of five sensation levels (10, 20, 30, 40, and 50 dB). The masking curves from this procedure are frequently referred to as "psychophysical tuning curves" and provide an indication of frequency selectivity. The results are compared with analogous data in other species and suggest that frequency analysis in the parakeet ear is somewhat less accurate than in the mammalian ear.     

An automated positive reward method for measuring acoustic sensitivity in fish

A microcomputer-controlled positive reward operant conditioning paradigm was developed to measure auditory sensitivity of the goldfish (Carassius auratus). Although other procedures have been used to measure hearing sensitivity in fish, all earlier studies have been done with some form of aversive conditioning. Goldfish were trained with a positive reinforcement method to determine hearing thresholds at 200, 500, 1000, 1500, and 2000 Hz. The audiogram obtained in this study is in close agreement with thresholds obtained with instrumental avoidance and classical conditioning procedures involving negative reinforcement (shock). The similarity in threshold data validates the effectiveness of the positive reinforcement paradigm described here. The major advantages of the present paradigm are the following: (1) No physical punishment such as electric shock is used, and (2) the versatility of the system allows easy modification for a variety of experiments.     

The variance of d' estimates obtained in yes-no and two-interval forced choice procedures

In studies of detection and discrimination, data are often obtained in the form of a 2 x 2 matrix and then converted to an estimate of d' based on the assumptions that the underlying decision distributions are Gaussian and equal in variance. The statistical properties of the estimate of d', d' are well understood for data obtained using the yes-no procedure, but less effort has been devoted to the more commonly used two-interval forced choice (2IFC) procedure. The variance associated with d' is a function of true d' in both procedures, but for small values of true d' the variance of d' obtained using the 2IFC procedure is predicted to be less than the variance of d' obtained using yes-no; for large values of true d', the variance of d' obtained using the 2IFC procedure is predicted to be greater than the variance of d' from yes-no. These results follow from standard assumptions about the relationship between the two procedures. The present paper reviews the statistical properties of d' obtained using the two standard procedures and compares estimates of the variance of d' as a function of true d' with the variance observed in values of d' obtained with a 2IFC procedure.     

Measures of response bias at minimum-detectable luminance levels in the pigeon

Using an operant analogue of the yes-no detection task, six pigeons were trained to detect luminance changes under two different reinforcement-scheduling procedures. In the first, an uncontrolled reinforcement-ratio procedure, the relative frequency of food reinforcers obtained for correct detections was free to vary with the birds' behavior as luminance levels were changed. In the second, a controlled reinforcement-ratio procedure, changes in preference could not alter the relative distribution of food reinforcers between the two response alternatives. Extreme response biases developed as luminance was decreased to threshold in the uncontrolled procedure. No progressive changes in response bias as a function of decreasing luminance were seen in the controlled procedure. Absolute thresholds for light intensity were lower in the controlled than in the uncontrolled procedure.     

Contrast discrimination by the methods of adjustment and two-alternative forced choice

Fifty years after the advent of signal-detection theory, some visual scientists still adhere to the notion of a high, fixed threshold. Indeed, experienced observers are able to deliver consistent settings of thresholds using the method of adjustment, but those settings are different from the thresholds obtained with two-alternative forced choice (2AFC) procedures. This article illustrates the difference by reference to four existing studies of contrast discrimination. All four sets of data show clear subthreshold facilitation, but the method of adjustment produces a rectilinear characteristic that corresponds to the use of different criteria over different ranges of contrast, whereas 2AFC procedures produce a curvilinear characteristic with generally lower thresholds. This article proposes a theoretical explanation for the difference.     

Semantic priming without awareness: Some methodological considerations and replications

Previous studies of subliminal semantic priming effects are considered. The distinction between subjective and objective detection thresholds proposed by Cheesman and Merikle (1984) is accepted, and it is concluded that no convincing evidence has been adduced to support or deny the existence of semantic priming effects at or below objective threshold. New criteria for the assessment of objective thresholds are proposed, and four experiments are reported in each of which pattern-masked primes were presented 10% below objective threshold. The first three experiments presented primes, mask, and targets binocularly; the fourth used dichoptic presentation. Data were analysed using both conventional F ratios and the quasi F ratio advocated by Clark (1973). Results showed that significant subliminal semantic priming effects occurred in each experiment when conventional F ratios were used, and significant effects occurred in all but the first experiment when quasi F was used. Binocular and dichoptic presentation of stimuli gave semantic priming effects whose magnitudes did not differ significantly. It is concluded that semantic priming effects can be obtained below objective detection threshold. It is also concluded that replication with different participants and different stimuli is preferable to the use of quasi F ratios in investigations where verbal stimuli are used.     

Echoic memory and language perception

The purpose of this study was to analyze asymmetry in echoic memory as a relevant factor in language perception. Two experimental procedures were used: the presentation of temporally segmented words in fragments of 40, 80, 120 and 240 msec, separated by intervals of 40, 80, 120 and 240 msec, similar to the procedures used by A. W. F. Huggins (1975, Perception & Psychophysics, 18, 149-157); the presentation of two tones of short duration, "high" and "low," followed by an interference tone equivalent to the mean frequency of the two tones, closely following the procedure used by D. W. Massaro (1975, in D.W. Massaro (Ed.), Understanding language, New York: Academic Press). A stereophonic tape recorder was used as follows: one channel was employed for the presentation of the words or tones while, through the other channel, the subject received a white noise equivalent in intensity. All subjects carried out the task twice (right ear, left ear) and the order of presentation was counterbalanced. Only the first task showed differences between ears. Implications of the results are analyzed.