Severe Departure Research Articles

Detection of tones in noise and the "severe departure" from Weber's law.

Thresholds were measured for the detection of 20-ms sinusoids, with frequencies 500, 4000, or 6500 Hz, presented in bursts of bandpass noise of the same duration and centered around the signal frequency. A range of noise levels from 35 to 80 dB SPL was used. Noise at different center frequencies was equated in terms of the total noise power in an assumed auditory filter centered on the signal frequency. Thresholds were expressed as the signal levels, relative to these noise levels, necessary for subjects to achieve 71% correct. For 500-Hz signals, thresholds were about 5 dB regardless of noise level. For 6500-Hz signals, thresholds reached a maximum of 14 dB at intermediate noise levels of 55-65 dB SPL. For 4000-Hz signals, a maximum threshold of 10 dB was observed for noise levels of 45-55 dB SPL. When the bandpass noises were presented continuously, however, thresholds for 6500-Hz, 20-ms signals remained low (about 1 dB) and constant across level. These results are similar to those obtained for the intensity discrimination of brief tones in bandstop noise [R. P. Carlyon and B. C. J. Moore, J. Acoust. Soc. Am. 76, 1369-1376 (1984); R. P. Carlyon and B. C. J. Moore, J. Acoust. Soc. Am. 79, 453-460 (1986)].

Continuous versus gated pedestals and the "severe departure" from Weber's law.

Thresholds were compared for the detection of 20-ms sinusoidal signals presented with either continuous or gated sinusoidal pedestals of the same frequency (500 or 6500 Hz). Pedestal levels ranged from 35-80 dB SPL. For 500-Hz signals, thresholds were lower in the continuous-pedestal condition than in the gated-pedestal condition, for all pedestal levels above 35 dB SPL. When the pedestal level was 35 dB, thresholds were higher in the continuous-pedestal condition than in the gated-pedestal condition. This was also true at all pedestal levels when bandstop noise centered around the pedestal frequency was added to the pedestal. For 6500-Hz signals, a deterioration in performance at intermediate levels, similar to that reported by Carlyon and Moore [J. Acoust. Soc. Am. 76, 1369-1376 (1984)], was found in the gated-pedestal condition. No such deterioration occurred in the continuous-pedestal condition. However, masking signal onsets and offsets by bursts of bandpass noise produced a midlevel deterioration in the continuous-pedestal condition. This was true when bandstop noise was absent, and when it was gated on and off in each observation interval. When continuous bandstop noise was present, no midlevel deterioration was observed, even when onsets and offsets were masked. The results suggest that in the continuous-pedestal condition subjects may normally maintain performance across level at 6500 Hz by attending to a transient response to signal onsets. Presenting bursts of bandpass noise disrupts the detection of such a response. The absence of a midlevel deterioration when continuous bandstop noise was present may be related to the adaptation to the sinusoidal pedestal that was caused by the bandstop noise.

Intensity discrimination: a severe departure from Weber's law.

These experiments were designed to assess the importance of different types of information which might be used in detecting intensity changes for pure tones. Thresholds for detecting an intensity change, expressed as 10 log (delta I/I), were measured over a wide range of frequencies and levels under conditions where one or more sources of information was either present or was removed. Spread of excitation was restricted by using bandstop noise centered at the signal frequency. Information conveyed by dynamic responses to signal onsets and offsets was eliminated by masking onsets and offsets with bursts of bandpass noise. Phase-locking information was eliminated by using high-frequency signals (above 5 kHz). Dynamic responses to signal onsets and offsets appear to play little role in intensity discrimination. Phase locking does appear to be important since Weber's law or a near-miss to it was observed at low frequencies, whereas at high frequencies performance deteriorated at moderate sound levels, and improved again at high levels. A preliminary experiment, using 225-ms stimuli revealed only a small midlevel deterioration at high frequencies. However, when 30-ms stimuli were used a large deterioration was observed, performance being worse when bandstop noise was presented with the tone. Hence at short durations and high frequencies spread of excitation seems to be important: When it is restricted by bandstop noise values of 10 log (delta I/I) observed at moderate levels it can be as large as 14 dB. The results of the experiments are consistent with a bimodal distribution of thresholds in primary auditory neurons; at intermediate levels neither population will operate effectively.(ABSTRACT TRUNCATED AT 250 WORDS)

A severe departure from Weber's law

Intensity discrimination for 225‐ms sinusoids with frequencies of 500, 4000, and 6500 Hz was measured at 25, 55, and 85 dB SPL both in the presence and absence of band‐reject noise centered at the signal frequency. For the lower two frequencies Weber's law, or a near miss to it, was obtained. At 6500 Hz the Weber fraction increased from 25 to 55 dB and decreased again at 85 dB both in the presence and absence of band‐reject noise. Removing intensity information conveyed by dynamic responses to stimulus onsets, by masking tone onsets with short burst of bandpass noise, had no effect. Reducing duration to 30 ms greatly increased the deterioration at 55 dB and 6500 Hz, but had little effect at other level/frequency combinations. The results are consistent with a bimodal distribution of thresholds in primary auditory neurons. The absence of a level effect at the lower two frequencies may be explained by phase‐locking cues extending the range over which VIIth nerve fibers can signal changes in intensity [Work supported by SERC.]

Models of mania: An individual case study.

SummaryA longitudinal study of a single case of manic-depressive psychosis investigated the relationship between psychiatric ratings, reaction time and two measures of autonomic activity. Measurements were made on 19 occasions over a five-month period. The number of slow responses on the reaction time task increased with increasing depression. Manic periods appeared not to be characterized by a slowing of responses, but rather by an increase in the number of premature responses, i.e. those made to the warning signal. A derived performance index discriminated over the complete range from severe depression to severe mania.Increased depression was associated with lower heart rate resting levels, and increasing mania with increased skin conductance levels. An increased frequency of slow reaction times was significantly associated with lower resting heart rate. Skin conductance measures correlated significantly with the number of premature responses made on the reaction time tasks. Some differences in the relationships emerged when data obtained during the administration of lithium were included in the analysis.The results are discussed in relation to both the bipolar and the continuum models of manic-depressive psychosis. The latter model is not supported by the present investigation, since manic episodes were not characterized by a more severe departure from normality than depressive episodes on either the number of slowed responses or autonomic measures.

USSR CRAFT AND TECHNICAL TRAINING — 1

Recent studies in the USSR reveal the provision of full‐time further education and training courses up to three years in length for all the more skilled trades. These normally involve severe specialisation and complete departure from traditional forms of apprenticeship

Reinforced concrete under thermal gradients

Summary The significance and current knowledge of thermal effects in concrete and reinforced concrete are reviewed briefly. It is evident that there is a need for more basic data on the shrinkage and creep of concrete subjected to high temperatures. Tests designed to obtain some of these data are described; results for the shrinkage and creep of a particular concrete at temperatures up to l40°C are presented. Some of the specimens were sealed to prevent loss of moisture, to simulate the conditions in mass concrete. It is shown that the time-dependent strains are markedly temperature-dependent. The paper then describes tests on model reinforced concrete beams subjected to a thermal gradient while flexurally restrained but without longitudinal restraint. The behaviour of the unsealed beams showed a severe departure from the predictions of conventional elastic theory, even to the extent of indicating compression in the reinforcing steel, instead of the expected tension. This was due to shrinkage and creep under the high temperatures. The behaviour of the sealed reinforced concrete specimens approximated to the predictions of elastic theory with a low value of the elastic modulus. A numerical procedure for estimating approximately the effects of time- and temperature-dependent strains in flexurally restrained beams is outlined in an Appendix.

Thermodynamics of Crystallization in High Polymers. I. Crystallization Induced by Stretching

A theory of oriented crystallization in elongated polymers having network structures (e.g., in vulcanized rubber) is developed through the application of statistical mechanical procedures similar to those employed in rubber elasticity theory. Expressions are derived which, within the limitation imposed by the simplifying assumptions, relate the incipient crystallization temperature with the elongation, the degree of crystallinity with the elongation and temperature, and the retractive force at crystallization equilibrium with the elongation at constant temperature. The reciprocal of the absolute temperature for incipient crystallization is predicted to decrease linearly with a simple function of the elongation and the average number of chain segments between cross linkages. Only moderate degrees of crystallinity are predicted at equilibrium. In conformity with requirements of the second law of thermodynamics, equilibrium crystallization decreases the tension in the stretched specimen. Apparent discrepancies between some of these predictions and various observations are attributed to severe departure from equilibrium crystallization when the polymer undergoes crystallization during the stretching process. A better approach to equilibrium should be achieved by stretching under conditions which prevent crystallization (e.g., at elevated temperature), then allowing crystallization to proceed at fixed elongation. Few experiments have been performed in this manner, but such results as are available confirm qualitatively the predictions of the theory. Reasons for the rapid increase in tension which is observed when crystallization occurs during ordinary stretching of rubber are discussed. It is pointed out that crystalline and amorphous regions preferably should not be regarded as separate phases. Likewise, the conversion of amorphous to crystalline polymer does not conform to the definition of a phase transition.