Superradiance for Atoms Trapped along a Photonic Crystal Waveguide

We report observations of superradiance for atoms trapped in the near field of a photonic crystal waveguide (PCW). By fabricating the PCW with a band edge near the D(1) transition of atomic cesium, strong interaction is achieved between trapped atoms and guided-mode photons. Following short-pulse excitation, we record the decay of guided-mode emission and find a superradiant emission rate scaling as Γ̅(SR)∝N̅Γ(1D) for average atom number 0.19≲N̅≲2.6 atoms, where Γ(1D)/Γ'=1.0±0.1 is the peak single-atom radiative decay rate into the PCW guided mode, and Γ' is the radiative decay rate into all the other channels. These advances provide new tools for investigations of photon-mediated atom-atom interactions in the many-body regime.

Atom-light interactions in photonic crystals

The integration of nanophotonics and atomic physics has been a long-sought goal that would open new frontiers for optical physics, including novel quantum transport and many-body phenomena with photon-mediated atomic interactions. Reaching this goal requires surmounting diverse challenges in nanofabrication and atomic manipulation. Here we report the development of a novel integrated optical circuit with a photonic crystal capable of both localizing and interfacing atoms with guided photons. Optical bands of a photonic crystal waveguide are aligned with selected atomic transitions. From reflection spectra measured with average atom number N=1.1+/-0.4, we infer that atoms are localized within the waveguide by optical dipole forces. The fraction of single-atom radiative decay into the waveguide is Γ1D/Γ'≃(0.32±0.08), where Γ1D is the rate of emission into the guided mode and Γ' is the decay rate into all other channels. Γ1D/Γ' is unprecedented in all current atom-photon interfaces.

Enhancement of mechanical Q factors by optical trapping

The quality factor of a mechanical resonator is an important figure of merit for various sensing applications and for observing quantum behavior. Here, we demonstrate a technique to push the quality factor of a micromechanical resonator beyond conventional material and fabrication limits by using an optical field to stiffen or trap a particular motional mode. Optical forces increase the oscillation frequency by storing most of the mechanical energy in a nearly lossless optical potential, thereby strongly diluting the effect of material dissipation. By placing a 130 nm thick SiO2 pendulum in an optical standing wave, we achieve an increase in the pendulum center-of-mass frequency from 6.2 to 145 kHz. The corresponding quality factor increases 50-fold from its intrinsic value to a final value of Q=5.8(1.1)×10(5), representing more than an order of magnitude improvement over the conventional limits of SiO2 for this geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems.

Selective requirement for Src kinases during VEGF-induced angiogenesis and vascular permeability

Src kinase activity was found to protect endothelial cells from apoptosis during vascular endothelial growth factor (VEGF)-, but not basic fibroblast growth factor (bFGF)-, mediated angiogenesis in chick embryos and mice. In fact, retroviral targeting of kinase-deleted Src to tumor-associated blood vessels suppressed angiogenesis and the growth of a VEGF-producing tumor. Although mice lacking individual Src family kinases (SFKs) showed normal angiogenesis, mice deficient in pp60c-src or pp62c-yes showed no VEGF-induced vascular permeability (VP), yet fyn-/- mice displayed normal VP. In contrast, inflammation-mediated VP appeared normal in Src-deficient mice. Therefore, VEGF-, but not bFGF-, mediated angiogenesis requires SFK activity in general, whereas the VP activity of VEGF specifically depends on the SFKs, Src, or Yes.

VEGF upregulates ecNOS message, protein, and NO production in human endothelial cells

Vascular endothelial growth factor (VEGF) is an endothelium-specific secreted protein that potently stimulates vasodilation, microvascular hyperpermeability, and angiogenesis. Nitric oxide (NO) is also reported to modulate vascular tone, permeability, and capillary growth. Therefore, we hypothesized that VEGF might regulate endothelial production of NO. The production of nitrogen oxides by human umbilical vein endothelial cells (HUVECs) was measured after 1, 12, 24, and 48 h of incubation with VEGF. VEGF treatment resulted in both an acute (1 h) and chronic (> 24 h) stimulation of NO production. Furthermore, Western and Northern blotting revealed a VEGF-elicited, dose-dependent increase in the cellular content of endothelial cell nitric oxide synthase (ecNOS) message and protein that may account for the chronic upregulation of NO production elicited by VEGF. Finally, endothelial cells pretreated with VEGF for 24 h and subsequently exposed to A-23187 for 1 h produced NO at approximately twice the rate of cells that were not pretreated with VEGF. We conclude that VEGF upregulates ecNOS enzyme and elicits a biphasic stimulation of endothelial NO production.

Nitric oxide is an upstream signal of vascular endothelial growth factor-induced extracellular signal-regulated kinase1/2 activation in postcapillary endothelium

We recently demonstrated that nitric oxide (NO) significantly contributes to the mitogenic effect of vascular endothelial growth factor (VEGF), suggesting a role for the NO pathway in the signaling cascade following kinase-derivative receptor activation in vascular endothelium. The aim of this study was to investigate the intracellular pathways linked to VEGF/NO-induced endothelial cell proliferation. We assessed the activity of the mitogen-activated protein kinase (MAPK) that is specifically activated by growth factors, extracellular-regulated kinase (ERK1/2), on cultured microvascular endothelium isolated from coronary postcapillary venules. ERK1/2 was immunoprecipitated, and its activity was assessed with an immunocomplex kinase assay. In endothelial cells exposed for 5 min to the NO donor drug sodium nitroprusside at a concentration of 100 microM, ERK1/2 activity significantly increased. VEGF produced a time- and concentration-dependent activation of ERK1/2. Maximal activity was obtained after 5 min of stimulation at a concentration of 10 ng/ml. The specific MAPK kinase inhibitor PD 98059 abolished ERK1/2 activation and endothelial cell proliferation in a concentration-dependent manner in response to VEGF and sodium nitroprusside. The NO synthase inhibitor Nomega-monomethyl-L-arginine, as well as the guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, blocked the activation of ERK1/2 induced by VEGF, suggesting that NO and cGMP contributed to the VEGF-dependent ERK1/2 activation. These results demonstrate for the first time that kinase-derivative receptor activation triggers the NO synthase/guanylate cyclase pathway to activate the MAPK cascade and substantiates the hypothesis that the activation of ERK1/2 is necessary for VEGF-induced endothelial cell proliferation.

Stretch-activated single-channel and whole cell currents in vascular smooth muscle cells

Mechanosensitive ion channels may play a key role in transducing vascular smooth muscle (VSM) stretch into active force development. To test this hypothesis, we recorded single-channel and macroscopic currents during mechanical stimulation of enzymatically dispersed vascular smooth muscle cells. Patch pipette suction activated a nonselective cation channel that was permeable to K+, Na+, and Ca2+. Whole cell stretch was accomplished using two patch-type micropipettes attached to the cell ends with suction. Stretch elicited a sustained depolarization with a magnitude similar to that observed in pressurized arteries. Under whole cell voltage clamp, stretch activated an inward current with a reversal potential near -15 mV. In another series of experiments, whole cell stretch failed to modify the current-voltage relationship for voltage-gated calcium currents. Thus, in VSM, both single-channel and whole cell data are consistent with activation of a nonselective cation channel by stretch. This mechanism may, in part, account for pressure-induced activation of intact blood vessels.

A novel series of milbemycin antibiotics from Streptomyces strain E225. II. Isolation, characterization, structure elucidation and solution conformations

A novel series of milbemycin antibiotics were isolated from the fermentation broth of a Streptomyces species designated E225. The structures of the four main metabolites VM 44857 (1), VM 44864 (2), VM 44865 (3) and VM 44866 (4) were determined by NMR techniques. In addition we describe the solution conformations of the major metabolite VM 44857 (1).

Visual control of balance in cerebellar and parkinsonian syndromes

The role of vision in the control of balance in patients with Parkinson's disease (PD) and cerebellar disease (CD) was studied by measuring body sway with eyes open, closed, and in response to visual stimuli generated by discrete lateral displacements of a moveable room which enclosed the subjects. In response to room movement, normal subjects swayed by an amount intermediate between sway with eyes open and eyes closed and their response attenuated on repetition of the movement, a process depending on shifting from predominantly visual to proprioceptive control. CD patients swayed more than controls with eyes open or closed and as shown by high 'Romberg quotients' (eyes closed/eyes open sway ratio) were able to use visual information to control much of their unsteadiness. CD patients had a normal attenuation of response to repetition of the room movement. PD patients had normal sway with eyes open or closed but their responses to room movement were abnormal, being proportionately larger and failing to attenuate during successive stimuli. The results indicate that cerebellar lesions seem largely to spare the visuopostural loop and also spare the ability to shift from a visual to a proprioceptive control of postural sway. In contrast, the findings in PD suggest that the visuopostural loop is hyperactive and that its influence cannot easily be de-emphasized when visual information is misleading. The latter finding suggests that basal ganglia participation in posture is concerned with the reweighting of the various sensorimotor loops controlling posture in the process of adapting to novel situations.

The functional significance of auditory adaptation

If a short duration pulse is added periodically every 30 s to a continuous tone, then the loudness of the continuous tone, which would otherwise remain unchanged, appears to undergo a progressive decline over a period of 3 min. The question at issue is whether the loss of loudness is actually induced by the pulse or merely made obvious. In support of the latter proposition a model has been developed which indicates how the loudness difference between the pulsed and continuous tone will increase as a result of adaptation. However, the model also predicts that a loudness loss should, in addition, be apparent in the pulsed tone itself. This has been confirmed by balancing the loudness in one ear of a 10 dB increment to a continuous tone of 60 dB at 1 kHz with an intermittent pulsed tone of the same frequency in the other. The magnitude of the loudness loss (of the order of 5 dB) accords well with the model prediction. The functional implications are that adaptation of continuous background noise should serve to reduce its masking effect upon speech and other transitory auditory stimuli rendering them more easily detectable.

The pattern of consonant and vowel errors in patients with conductive and cochlear hearing loss

An analysis was carried out of the pattern of errors in those words which were incorrectly perceived by patients during the course of routine speech audiometric tests using consonant-vowel-consonant words. Responses were examined from 20 patients with conductive hearing loss, and 20 with cochlear hearing loss due to Ménière's disease. Word errors result from misinterpretations of a single consonant in 70% of the conductive group and 56% of the Ménière group. The latter make slightly more errors involving both consonants. Errors in vowels alone are rare in both groups and, even in combination, with one or other consonant, never exceed 25%. Word recognition appears to fail for the same reason in the two groups.

Effect of simulated bilateral cochlear distortion on speech discrimination in normal subjects

Bilateral sensorineural hearing loss may introduce grossly dissimilar cochlear distortion at the two ears, causing abnormal demands to be made upon the cortical analytical centres which normally receive congruent information. As a result, the prescription of binaural hearing aids may be a handicap rather than a help. In order to explore this possibility, 10 normal subjects were presented with simulated, dissimilar cochlear distortion at the two ears. Discrimination scores with binaural presentation were poorer than the best monaural score and there were clear indications that in the former, subjects selectively attended to one ear and neglected the other. In contrast, binaural presentation of the same simulated distortion resulted in a significant improvement, compared with the monaural discrimination score. Inability of the cortex to contend with discongruent speech input from the two ears may be a factor contributing to the rejection of binaural hearing aids in some individuals.

A novel series of milbemycin antibiotics from Streptomyces strain E225. I. Discovery, fermentation and anthelmintic activity

A novel series of milbemycin antibiotics were produced by soil isolate, strain E225 which was shown to be a Streptomyces species. The antibiotics displayed anthelmintic activity against Trichostrongylus colubriformis in the gerbil. Two of the compounds, VM 44857 and VM 44866 were shown to be potent anthelmintics against mixed nematode infections in sheep.

Evidence of direct thermal action upon the vestibular receptors in the caloric test. A re-interpretation of the data of Coats and Smith

Although Bárány's convection theory has gained wide acceptance, there is strong evidence that the caloric response may include a component resulting from direct thermal stimulation of the vestibular end organs. It is argued on theoretical grounds that important new information could be obtained from a precise determination of the neutral head positions at which caloric irrigation fails to elicit a response. Although experimental studies using a bracketing procedure proved unsuccessful for this purpose, a re-examination of the extensive studies of Coats and Smith revealed that this information was already available. Reinterpreted in this way, their data clearly indicate that the hot and cold components resulting from direct thermal action equate to 42% and 34% respectively of the responses obtained in the planes of maximum reactivity. This is of sufficient magnitude to account for the anomalous findings in Spacelab I. Because of non-linearity in the relationship between neural discharge evoked by caloric irrigation and nystagmus magnitude, this component may be significantly less in the conventional caloric position. For this and other reasons there would seem to be no good reason to re-evaluate the clinical reliability of the caloric test.

Observations bearing upon semi-circular canal dynamics

It can be shown that following an angular velocity step stimulus delivered in darkness, the nystagmic responses can be effectively 'dumped' after any interval in time by the application of an appropriate step decrement in velocity. In practise the null velocity is bracketed between those step decrements inducing just detectable nystagmus to left and right and can be determined within a range of +/- 1.5 degrees s-1. With test stimuli of 22, 44, and 64 degrees s-1 the 'dump' velocities have been established at varying intervals in time on four normal subjects. Contrary to expectations the dump velocity/time relations for all three test stimuli follow a convergent linear course. The dump velocities are unaffected by fixation suppression of the nystagmus induced by the test stimuli. The seeming irrelevance of nystagmus generation to dump velocity values is confirmed by the good correspondence with the results of a separate study using the oculogyral illusion as a guide in place of nystagmus. These findings are difficult to relate to conventional concepts of cupular dynamics.

Transfer of optokinetic activity to vestibular nystagmus

Transfer of activity generated by prior optokinetic (OK) stimuli of one minute's duration to nystagmus induced in darkness by a subsequent vestibular stimulus consisting of step velocities to and from 40 degrees/s-1 was studied in 10 normal subjects. Four types of OK stimuli were used: (a) full field 'passive'; (b) full field 'active'; (c) full field in the presence of optic fixation, and (d) small OK drum stimulation. Transfer (T) was evident under all conditions and resulted in an enhancement of the vestibulo-ocular (VO) response when activity from the two stimuli were in the same direction (S) and a suppression when in the opposite (O). Expressed by the equation: Formula See Text. the respective transfer values obtained for the above conditions were (a) 66%, (b) 58%, (c) 22%, and (d) 54%. In all tests, rightward OK drum movement was more effective than leftward. In respect of passive OKN the resultant response can be well represented as the algebraic summation of the expected optokinetic after-nystagmus (OKAN) and the VO response, though opposing OKAN is more effective than enhancing. Passive OKN is more effective than active and this can be accounted for by the small contribution made by retinal slip in the former (the indirect path). Surprisingly, the small drum proved almost as effective as active OKN in terms of transfer. Fixation in the presence of full-field OK stimuli induces a non-directionally specific depression of the subsequent VO response, implying that retinal slip could contribute to the mechanism of VO response suppression.

Oscillopsia of peripheral vestibular origin. Central and cervical compensatory mechanisms

Eight patients with absent vestibular function categorized into four grades according to the disability they suffered from oscillopsia have been studied with a view to correlating its severity with the development of gaze stabilizing compensatory mechanisms. Eye movements were recorded while the following sinusoidal rotational stimuli were delivered: 1) trunk on head oscillation in the dark (COR); 2) head on trunk oscillation in the dark; 3) head on trunk and whole body (head and trunk) oscillation in the light in the presence of optic fixation. The COR was potentiated in all the patients regardless of their clinical status. Velocity gains (peak slow phase eye velocity/peak head velocity) during whole body rotation were significantly lower than head on trunk gains in the light in the better compensated patients. Since in the absence of vestibular function whole body rotation involves only the otokinetic system (OKN), this finding implies a depression of the OKN in these patients which can be corrected during head on trunk movements by virtue of a dynamic input from the neck. The results suggest that the processes of recovery from oscillopsia are dependent, in the main, upon the development of central mechanisms by means of which undesirable image movement across the retina is perceptually suppressed. Depression of OKN may be secondary to this perceptual rearrangement.

Hearing acuity and susceptibility to noise-induced hearing loss

Above a critical level (CL) of fatiguing tone, temporary threshold shift (TTS) rises rapidly with intensity. Using a fatiguing tone of 1000 Hz, threshold shift following 1 min stimulation at varying intensities was measured at the same frequency in 55 normal subjects and the CL determined for each. In a second and more limited study, TTS was measured at a frequency half an octave above that of the fatiguing tone. A significant inverse correlation was established between hearing level (HL) and CL at the same frequency with a fall of 2.5 dB in the latter for every 10 dB rise in the former. CLs measured half an octave above the fatiguing tone frequency were appreciably lower by 5 to 11 dB. No correlation was apparent between TTS and HTL, implying that TTS and CL are subserved by differing physiological mechanisms. The findings have relevance to the topic of susceptibility to noise-induced hearing loss and the formulation of damage risk criteria.

New perspectives in the investigation of disorders of balance

It is a common misconception that all disorders of balance can be attributed to derangements of the vestibular system. In fact spatial orientation is dependent upon the proper coordination of a number of sensory inputs and each of these is susceptible to damage by disease or injury. A variety of new tests is described which have as their aim the indentification of balance disorders resulting specifically from derangements of visual processing, proprioception and the neck reflexes. In addition, attention is given to the differential impairment of linear and circular vection and to the possible clinical application of vestibular evoked potentials.

The cervico-ocular reflex in normal subjects and patients with absent vestibular function

The role of the cervico-ocular reflex (COR) has been studied in 12 patients with absent vestibular function and 13 normal subjects. Ramp and sinusoidal displacement stimuli were applied with trunk on head and head on trunk movements. In all patients, trunk on head movements evoked a marked slow-phase compensatory COR while in normal subjects it was weak and variable in direction. Fast components of the COR induced gaze shifts in the direction of the relative head movement ('anticompensatory' direction) which could be suppressed by imagining an earth fixed targed. No tonic component could be identified instead, in the case of ramp stimuli, a residual eye deviation was noted which was significantly enhanced in the patients and resulted from activity dynamically generated during the course of the trunk movement and not from its final angular displacement. Head on trunk ramp displacements in the dark evoked initial anticompensatory saccades followed by slow compensatory components, a pattern of eye movements remarkably similar to that seen during active head-eye target seeking. Thus, in the absence of labyrinthine function, the COR appears to take on the role of the vestibulo-ocular reflex in head-eye coordination in the initiation of the anticompensatory saccade which takes the eyes in the direction of the target, and the generation of the subsequent slow compensatory eye movements. Central pre-programming, as revealed by comparing the effect of different instructions and active versus passive neck-induced eye movements, has a profound influence on COR functioning.

Observations upon the evoked responses to natural vestibular stimulation

Repetitive rotational stimuli simulating natural head movements have been applied to the study of the vestibular evoked response in normal subjects and 12 patients with complete loss of vestibular function. Special precautions were taken to eliminate all possible sources of artefacts, in particular, all eye movements were restrained by requiring the subject to fixate upon a target light attached to the rotating chair throughout the course of the test. With a stimulus of 2 sec duration the typical response took the form of a slow negative wave with a mean peak amplitude of approximately 24 microV and maximally recorded from the vertex. It was characteristically absent in the patient group. Occasionally, both in normal subjects and patients it was preceded by a long latency complex thought to be non-vestibular in origin. Tests carried out both in total darkness and in the light show a statistically significant increase in the potential in the latter condition indicating an influence of the optokinetic effect exerted by the visual surround. Further studies have explored the phase changes brought about by varying the amplitude and duration of the stimulus. These have revealed certain parallels in the results of recent animal experimental studies.

Cervical nystagmus due to loss of cerebellar inhibition on the cervico-ocular reflex: a case report

Studies of the cervico-ocular reflex and the vestibulo-ocular reflex have been carried out separately and in combination on a patient with gait ataxia due to a cerebellar tumour. With the head fixed in space, body rotation to the right (left neck torsion) induced marked nystagmus to the left in darkness. Vestibulo-ocular responses to sinusoidal rotation were symmetrical while the neck was immobilised and asymmetric when it moved freely. It is suggested that the cervical nystagmus seen in this case was the result of removal of cerebellar inhibition upon the cervico-ocular reflex and that abnormal interaction of cervical and vestibular inputs could have played a role in the patient's unsteadiness.

Neuro-otological manifestations of migraine

Vestibulocochlear derangements have been studied in three groups of patients: 200 unselected patients with migraine (Series I), 80 migrainous patients referred because of their symptoms for full neuro-otological examination (Series II), and 116 patients with tension headache who served as controls (Series III). Significant differences were established between tension headache and migraine in respect of incidence and severity of symptoms and their time of onset in relation to the headache. In migraine, vestibulocochlear disturbances can occur as an aura, accompanying the headache or during headache-free periods, the highest incidence occurring during the headache. In Series I, 59 per cent reported vestibular and/or cochlear symptoms and these were of disabling severity in 5 per cent. Significantly, 50 per cent had a history of motion sickness and 81 per cent experienced phonophobia during the headache, the probable mechanism of which is discussed. Persisting vestibulocochlear derangements were found in 77.5 per cent of Series II, largely vestibular and of both central and peripheral origin. Involvement of the vertebrobasilar vascular system appears to be the most likely explanation. Possible links between Ménière's disease, benign paroxysmal vertigo and migraine are discussed.

Tonal adaptation

The loudness of a continuous pure tone does not appear to change with time unless an interrupted tone is introduced at intervals during the course of the test; in consequence it is held that it is the interrupted tone which induces the loudness loss. This, however, cannot be called on to account for the marked change in quality or 'timbre' of a sustained pure tone which occurs over a period of time and which has the attributes of 'tonal adaptation', matching the time course of loudness adaptation revealed by dichotic loudness balance and other procedures. It is argued that the latter have to do with the measurement of sensation while judgement of the loudness of a continuous tone in isolation involves higher-order perceptual processes.

Speech discrimination in bilateral and unilateral hearing loss due to Ménière's disease

A comparison of the speech audiograms of patients with bilateral and unilateral hearing loss due to Menière's disease has shown that when matched in respect of pure-tone hearing levels, speech discrimination at the better ear of the former is appreciably better than that at the impaired ear of the latter. In addition, while roll-over is a characteristic feature of the unilateral group it is conspicuously absent in the bilateral group. More surprisingly, in the bilateral group, despite relatively small differences in the pure-tone hearing levels at the two ears, speech discrimination at the better ear is strikingly superior to that at the poorer ear. It is concluded that patients with bilateral hearing loss selectively make use of the better ear to the neglect of the poorer ear. This could have important implications in the prescription of binaural hearing aids.

Influence of peripheral vision upon vestibulo-ocular reflex suppression

The effect of peripheral vision upon the suppression of caloric induced nystagmus has been studied in normal subjects and patients with Parkinson's disease and cerebellar lesions. In normal subjects, caloric responses in the presence of optic fixation upon a target light viewed in darkness are further suppressed by a factor of two when background illumination is introduced. In both patient groups background illumination had significantly less effect. Additionally, optokinetic and pursuit test have revealed specific abnormalities consistent with the notion of a peripheral retinal feed-back mechanism deranged by disease. These in turn appear to have particular relevance to certain visuo-vestibular disturbances characteristic of patients in both groups.

Vestibular and optokinetic evoked potentials

Earlier studies of vestibular evoked potentials have adopted the expedient of rotating subjects with eyes closed and in consequences there exists a suspicion that the responses obtained might have been contaminated by corneo-retinal potentials. In order to minimise this artefact, subjects were required to fixate upon a small target light attached to and rotating with the chair while in total darkness. The rotational stimulus was a controlled angular rotation of the chair simulating a normal head movement. Averaged responses of ten such stimuli have revealed a consistent and well defined characteristic wave form not present in six patients with total vestibular loss. Similar evoked responses were obtained to a full field optokinetic stimulus approximating to that of the movement of the chair. Combined optokinetic and vestibular stimulation does not show algebraic summation. The evoked responses have features in common with nervous activity recorded in the monkey at vestibular nuclei and thalamic levels in comparable test situations.

Loudness adaptation: real or illusory

There is general agreement that, except at low sensation levels, the loudness of a continuous pure tone does not appear to change with time. By contrast, using a simultaneous dichotic loudness balancing procedure (SDLB) a substantial fall in loudness can be revealed. As a result it has been held that the latter does not represent a loudness loss in real terms but is a manifestation of some form of central binaural interaction possibly involving localization mechanisms. In two studies reported here, one involving a loudness scaling procedure using as a standard a reference tone of 65 dB (HL) and the other a loudness doubling procedure, a loudness loss has been clearly demonstrated following sustained stimulation with a continuous 60-dB (HL), 1000-Hz tone applied monaurally. The progression of the loudness loss with time follows a similar course to that found with the SDLB procedure. In consequence it is concluded that both represent a loudness loss in real terms and that inability to detect a change in loudness over time of a continuous tone results from the absence of any reference standard by which it can be judged.