Detection Of Decrements Research Articles

Effect of sawtooth polarity on chromatic and luminance detection.

Psychophysical studies have documented that many observers show lower thresholds for rapid-off than for rapid-on sawtooth luminance modulation. This finding, together with physiological findings from chromatically opponent ganglion cells of the macaque monkey, prompted a search for a similar bias in psychophysical detection of chromatic increments and decrements of light. Using a luminance pedestal in conjunction with a luminance background to favor detection by chromatic mechanisms, we measured spectral sensitivity for rapid-on and rapid-off sawtooth stimuli presented spatially coextensive with the pedestal. There were two different pedestal chromaticities: one broadband, and the second composed only of long-wavelength light to enhance short-wavelength-sensitive, cone-mediated detection. Spectral-sensitivity measurements for different wavelength stimuli revealed no systematic differences across the visible spectrum as a function of sawtooth waveform polarity or pedestal chromaticity. Similarly, temporal contrast-sensitivity functions for hetero-chromatically modulated red-green sawtooth stimuli did not reveal an asymmetry in sensitivity for rapid-red and rapid-green chromatic change. Some of the observers showed a higher sensitivity for luminance modulated rapid-off sawtooth stimuli, as also noted in previous studies. This asymmetry was not found when a white luminance pedestal and background was used. These results suggest that the cone inputs to chromatically opponent ON- and OFF-center cells are sufficiently balanced to provide equivalent psychophysical thresholds for chromatic increments and decrements of light.

Effects of frequency on the detection of decrements and increments in sinusoids

Thresholds for the detection of decrements in level of sinusoidal signals were measured as a function of decrement duration and of frequency (250, 1000, and 4000 Hz) in nine normally hearing subjects. Thresholds for detecting a brief increment in level were also measured. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the decrement or increment. Performance tended to improve with increasing frequency, for all decrement durations and for increment detection. The results were analyzed using a model consisting of an array of bandpass filters (the auditory filters), each followed by a nonlinearity, a sliding temporal integrator and a decision device. The analysis indicated that the worsening in performance with decreasing frequency can be attributed mainly to changes in the efficiency of the decision device following the temporal integrator; at lower frequencies a larger change is required at the output of the integrator for threshold to be reached. At 250 Hz, the effect of the auditory filter in ‘‘smoothing’’ the internal representation of the stimuli appears to be comparable to the effect of the temporal integrator, making it difficult to determine the characteristics of the integrator.

Detection of intensity decrements by the chinchilla.

Three monaural chinchillas were trained to detect intensity decrements in broadband noise (20 kHz) using a shock-avoidance conditioning procedure. The intensity decrements were presented at one of nine different durations between 2 and 35 ms at noise levels of 25, 45, and 65 dB SPL. At each intensity-duration combination, the level of the decrement was varied to obtain a decrement threshold. The minimal detectable decrement decreased from approximately 20 dB at the shortest duration to an asymptote of roughly 4 dB at approximately 30 ms. The data were modeled by a low-pass filter with an 11-ms time constant. The decrement detection function of the chinchilla is similar to that of humans. However, long-duration decrement thresholds are larger in the chinchilla, as would be predicted from the large intensity difference limen of the chinchilla. In general, there was little change in the decrement function across background intensities except that 2-ms decrements were not detected at the 25-dB SPL background intensity.

Detection of intensity decrements followed by increments

Data were collected from a modified decrement detection procedure in order to compare subject performance to the predictions of two decision statistics derived from the output of an envelope detector. At roughly the midpoint of each stimulus presentation, there was an intensity increment of the gated wideband noise carrier. The task was to detect an intensity decrement just preceding the increment in the signal interval of the 2IFC task. Decrement duration ranged from 2.5 to 40 ms. Increments of 3, 6, and 9 dB were used with the onset of the increment randomly occurring 150–300 ms from the stimulus onset. Decrement detection was also measured for conditions in which there was no increment. Best performance was obtained with the 3‐dB increment. With the 6‐ or 9‐dB increment, thresholds were significantly higher and showed less change as a function of decrement duration. Simulations based on the output of an envelope detector used either the variance or the ratio of the largest‐to‐smallest value as the decision statistic. For both statistics, simulations approximated subject performance in the conditions with no increment. Simulations, however, did not show the drop in performance with the 6‐ or 9‐dB increment, suggesting involvement of multiplicative internal noise in envelope detection. [Work supported by NIDCD and AFOSR.]

Detection of intensity decrements by the chinchilla

Three monaural chinchillas were trained to detect intensity decrements in broadband noise (20 kHz) using a shock-avoidance conditioning procedure. The intensity decrements were presented at one of nine different durations between 2 and 35 ms at noise levels of 25, 45, and 65 dB SPL. At each intensity-duration combination, the level of the decrement was varied to obtain a decrement threshold. The minimal detectable decrement decreased from approximately 20 dB at the shortest duration to an asymptote of roughly 4 dB at approximately 30 ms. The data were modeled by a low-pass filter with an 11-ms time constant. The decrement detection function of the chinchilla is similar to that of humans. However, long duration decrement thresholds are larger in the chinchilla, as would be predicted from the large intensity difference limen of the chinchilla. In general, there was little change in the decrement function across background intensities except that 2-ms decrements were not detected at the 25 dB SPL background intensity. [Research supported by grants RO1NS16761 and RO1NS23894.]

Detection of increments and decrements in modulation depth of SAM noise

Difference limens (DLs) for the modulation depth of a sinusoidally amplitude-modulated (SAM) wideband noise were measured using a two-interval forced-choice adaptive procedure. For increment detection the reference modulation depth (mr) was 0.0, 0.25, 0.50, or 0.75. For decrement detection, mr was 0.45, 0.60, 0.75, or 0.90. Modulation frequency was 2, 4, 64, or 512 Hz. The DL is defined as 10 log|mthr2 − mr2|, where mthr is the modulation depth just discriminable from mr. For mr = 0.0, the DLs (or “absolute” modulation thresholds) varied from −25 to −10 dB as modulation frequency varied from 2–512 Hz. As mr increased, the increment DL increased monotonically for each frequency from its absolute detection level to about −6 dB at mr = 0.75. These data are in good agreement with those of Wakefleld and Viemeister [J. Acoust. Soc. Am. Suppl. 1 72, S90 (1982)]. The decrement DLs overlay and extended the increment DL functions, although the DLs for the highest mr (0.90) decreased slightly (−10 dB). In a separate manipulation, no effect on the modulation onset phase on modulation depth discrimination was found. [Work supported by NIH.]

Sound intensity processing by the goldfish.

Capacities of the goldfish for intensity discrimination were studied using classical respiratory conditioning and a staircase psychophysical procedure. Physiological studies on single saccular (auditory) nerve fibers under similar stimulus conditions helped characterize the dimensions of neural activity used in intensity discrimination. Incremental intensity difference limens (IDLs in dB) for 160-ms increments in continuous noise, 500-ms noise bursts, and 500-ms, 800-Hz tone bursts are 2 to 3 dB, are independent of overall level, and vary with signal duration according to a power function with a slope averaging - 0.33. Noise decrements are relatively poorly detected and the silent gap detection threshold is about 35 ms. The IDLs for increments and decrements in an 800-Hz continuous tone are about 0.13 dB, are independent of duration, and are level dependent. Unlike mammalian auditory nerve fibers, some goldfish saccular fibers show variation in recovery time to tonal increments and decrements, and adaptation to a zero rate. Unit responses to tone increments and decrements show rate effects generally in accord with previous observations on intracellular epsp's in goldfish saccular fibers. Neurophysiological correlates of psychophysical intensity discrimination data suggest the following: (1) noise gap detection may be based on spike rate increments which follow gap offset; (2) detection of increments and decrements in continuous tones may be determined by steep low-pass filtering in peripheral neural channels which enhance the effects of spectral "splatter" toward the lower frequencies; (3) IDLs for pulsed signals of different duration can be predicted from the slopes of rate-intensity functions and spike rate variability in individual auditory nerve fibers; and (4) at different sound pressure levels, different populations of peripheral fibers provide the information used in intensity discrimination.

Quantum fluctuation limit in foveal vision

A unique test of the hypothesis that only quantum fluctuations limit the detectability of foveal luminance change is presented. 10.9′ dia target spots were incremented or decremented in luminance. ROC curves for detection of both luminance increments and decrements were measured and found to conform to theoretical curves predicted on the basis of Poisson distributions of photon arrival. Four different parameters of the ROC curves lead independently to estimates of quantum efficiency with values of about 2 × 10 −4 . The measured quantum efficiency increases by about a factor of 10, to as high as 0.018, when the target is reduced to 1.2′ dia. This is consistent with the view that lateral inhibition causes many of the photons caught from a large target to be ineffectual in the task of detecting the luminance change signal.

Detection and recognition of intensity changes in tone and noise: The detection-recognition disparity

Recognition of increments vs decrements in auditory intensity improves with signal duration, relative to detection of increments and decrements. This effect obtains whether the background stimulus is a tone, noise, or a tone with noise masker, and is largely uninfluenced by the rise time of the signals. These data are inconsistent with detection models in which the O makes only one sensory observation during each observation interval, but can be described in terms of a neural timing model in which transients play a critical role.

On the importance of considering the signal’s frequency spectrum: Some comments on Macmillans “Detection and recognition of increments and decrements in auditory intensity” experiment

In a recent experiment on tonal masking, Macmillan (1971) reported that recognition of increments and decrements improves relative to detection performance as signal duration is increased. It is suggested that this result is largely artifactual, inasmuch as Macmillan’s Os undoubtedly detected brief-duration signals by virtue of energy splatter produced by gating the signal on and off rectangularly. Since energy splatter produced by an increment is identical to that produced by a decrement, Os listening off frequency could not have possibly distinguished a brief increment from a decrement.

Change detection and off-frequency listening: A reply to Leshowitz and Wightman

Leshowitz and Wightman’s (1972) account of the fact that recognition of increments and decrements in intensity improves with signal duration relative to detection of increments and decrements is found wanting. Not only does their interpretation fail to explain the occurrence of the effect in several different stimulus situations, but it is inconsistent with the results of detection experiments in which either signal duration or the signal polarity is uncertain.

Detection and recognition of increments and decrements in auditory intensity

Os’ performance in the detection of increments and decrements in the intensity of a pure tone was compared with their performance in an increment-decrement recognition experiment. Recognition performance improved, relative to detection performance, as signal duration increased. This is surprising from the point of view of all stimulus models within signal detection theory. These data and others are described in terms of a change detection mechanism.

Detection of Increments and Decrements in Continuous White-Noise Background

Observers were presented with a two-alternative forced-choice (2AFC) task in which, in separate experimental runs, the signal consisted of either increments or decrements in a continuous white-noise background. Stimulus intensity differences that would yield a level of 75% correct response were determined for six naive observors by the PEST Technique (Parameter Estimation by Sequential Testing). Initially, decrements are more difficult to detect than are increments. With practice, however, detection of decrements improves more rapidly than does detection of increments, and initial differences tend to disappear. [Supported by National Research Council, Canada.]