Luminance-dependent changes in mesopic visual contrast sensitivity

Spatial and temporal modulation transfer functions have been measured as a function of luminance at scotopic and mesopic levels. It is found that throughout the scotopic range the data can be accounted for by a two process visual system, with the processes having the following properties. Simple excitatory processThis mechanism summates over somewhat less than 1 square degree of visual angle and over about 200 msec of time. These properties do not change with luminance, but the over-all sensitivity of the mechanism follows the De Vries-Rose law. The temporal properties of this mechanism follows those of the scotopic b-wave. At high luminances, the temporal, but not spatial, properties of this mechanism break down in a manner which had not been studied.Low-frequency inhibitory processThis process is manifest as a decrease in sensitivity from that of the simple excitatory process. Its effect is observed only when both spatial and temporal frequency are low, suggesting that it has a larger (perhaps 3 x) summation area in both space and time. The inhibitory process is not observed below a certain threshold luminance, which is highly dependent upon the configuration of the stimulus. For a suitable stimulus, this threshold will be well into the scotopic luminance range.It is suggested that these two processes represent psychophysical correlates of the centre and surround of retinal receptive fields.

Nuclear magnetic resonance shift reagents: evidence for different mechanisms of contact contributions to C shifts induced by nickel and cobalt acetylacetonates with saturated amines and alcohols

The pattern of (13)C and (1)H nuclear magnetic resonance (NMR) shift changes produced by complexation of cobalt and nickel acetylacetonates with amines and alcohols indicates that there is more than one mode of operation of the contact interaction. A large effect with alternating signs is important at the alpha and beta carbons, but this effect seems to be overlaid by another influence that appears to fall off monotonically as one proceeds away from the site of complexation.

Disparity processing of spatial frequencies in man

1. Adaptation to a high-contrast sine-wave grating has been shown previously by Blakemore & Campbell (1969) to raise the modulation required to detect a low-contrast grating that has the same or similar spatial frequency as the adapting grating.2. A similar adaptation effect occurs when the adaptation and test gratings are seen binocularly and are presented off the plane of fixation. When the gratings are not located on the plane of fixation, however, the greatest rise in threshold following adaptation occurs for test gratings presented in the same plane as the adapting grating. Thus, the neural mechanisms adapted to the high contrast patterns must be processing disparity information.3. The spatial frequency response of the disparity adaptation effect has been measured by adapting to gratings of different spatial frequencies presented at a given disparity, and comparing threshold elevations for identical test gratings presented in the same (disparate) plane as the adapting grating or in the plane of fixation.4. The unbiased adaptation effect specific to disparity is greatest for gratings whose periods are twice the disparity.5. There is no adaptation effect specific to disparity for individuals possessing only convergent or only divergent disparity mechanisms.6. The results suggest that disparity mechanisms make bar by bar correlations as opposed to edge by edge correlations and that narrow bar detectors feed small disparity mechanisms whereas wide bar detectors feed large disparity mechanisms.

Detection of delayed hypersensitivity in mice injected with ribonucleic acid-protein fractions of Salmonella typhimurium

Manifestations of delayed hypersensitivity (cell-mediated immunity) were found to be present in mice immunized with virulent Salmonella typhimurium SR-11 subfractions which contained appreciable concentrations of bacterial protein and in mice immunized with the living, attenuated RIA strain of S. typhimurium. Delayed hypersensitive responses were measured by footpad sensitivity in the immunized mice and in vitro by inhibition of spleen cell migration and by increase in (3)H-thymidine uptake by lymphoid cell populations when exposed to bacterial fractions rich in protein content.

Ribonucleic acid-protein fractions of virulent Salmonella typhimurium as protective immunogens

Mice were injected with virulent Salmonella typhimurium SR-11 subfractions containing varied amounts of ribonucleic acid (RNA) and protein or with living attenuated S. typhimurium RIA. In these mice, maximal resistance to lethal infection by 1,000 or 5,000 median lethal doses of S. typhimurium SR-11 was seen 2 to 3 weeks after immunization. The S. typhimurium RIA vaccine and a crude ethanol-precipitated RNA fraction (E-RNA) prepared from lysates of S. typhimurium SR-11 were the most efficient immunogens inducing protection against salmonellosis. The contribution of the components present in the E-RNA fractions to host protection against lethal salmonella infection was also examined. RNA-rich fractions (P-RNA) prepared from lysates of the virulent salmonellae contained several bands of protein when examined by disc electrophoresis. P-RNA fractions stimulated protective immunity in mice to infection with S. typhimurium SR-11 but to a much lesser degree than did the E-RNA fractions or strain RIA vaccine. Protein-rich fractions (NP), separated from E-RNA by salt precipitation, exhibited the same number and distribution of protein bands by disc electrophoresis as did the parent E-RNA fractions. Mixtures of either bovine liver soluble RNA or various synthetic polynucleotides and NP were examined, as was NP fraction alone, for the ability to confer protection in mice to challenge infections by the virulent strain of salmonella. Polyadenylic-uridylic acid plus NP conferred significant protective immunity to challenge infections in mice immunized with this mixture, being nearly as effective an immunogen as were the E-RNA fractions of S. typhimurium SR-11 or the attenuated S. typhimurium RIA.

Phoneme discrimination in older persons under varying signal-to-noise conditions

Two groups of subjects, 10 older than 60 years of age and 10 between the ages of 18 and 30, having essentially normal hearing for pure tones at the speech frequencies, identified 16 consonants in a CV context. These syllables were presented at six sensation levels of noise over four signal-to-noise ratios. An analysis of variance of the mean percent correct responses showed that the older group performed significantly more poorly than the younger group over all listening conditions. However, there was no difference in the relative performance between the two groups as either the sensation level (SL) of noise was increased or the signal-to-noise (S/N) ratio became poorer. An additional listening condition in which no noise was present in the signal and the syllables were presented at six sensation levels revealed results similar to the main experiment. Possible implications are presented.

Studies of temporal frequency adaptation in visual contrast sensitivity

1. A short adaptation to sinusoidal flicker produces a temporary elevation in the temporal contrast threshold of a human observer.2. The frequency specificity of this adaptation effect is much less than that observed with adaptation to spatial frequencies; thus it does not seem warranted to postulate the existence of distinct channels for the detection of specific temporal frequencies, as has been done in the case of spatial frequencies (Blakemore & Campbell, 1969).3. At low frequencies, a substantial adapting modulation is necessary to produce an effect, but at high frequencies an effect can be seen even with adaptation which is below threshold (as determined by the method of adjustment).4. This subthreshold adaptation appears to explain the observation that thresholds set by the method of adjustment rise by as much as a factor of two during the first minute of exposure.5. No interocular transfer of the adaptation effect was observed.6. Adaptation first appears at mesopic luminances, but its appearance is not dependent on the change from rod to cone vision. Under several conditions, however, the first appearance of flicker adaptation did coincide with a change in the deLange curve, which is attributable to the appearance of the antagonistic surround of visual receptive fields. Thus it was hypothesized that the surround is essential for adaptation.

Cure of lung cancer from incomplete surgical resection

Three patients with lung cancer have been cured by incomplete removal of the cancer, which has for 20 years been the policy of this unit when complete removal is not possible. In each patient residual cancer remained on the wall of the left atrial chamber of the heart at the end of an operation for pneumonectomy.Incomplete removal of cancer may, as a rare event, cure the patient. When residual cancer remained on any mediastinal structure other than the atrium cure has not been seen, though progress of the cancer seems to be retarted in some patients.

Reversal of malignant transformation by tumor DNA

Walker-256 carcinosarcoma cells grown in tissue culture medium containing inhibitory DNA prepared from the tumor are shown to have an unaltered growth in vitro, but a diminished capacity to produce malignant tumors on injection into the rat. Coincident with this change in virulence is the induction of tRNA methylase inhibitors in these malignant cells. Within days after the DNA is removed from the growth medium, the tRNA methylase inhibitors disappear and the oncogenicity reappears.

Vascular insufficiency and differential distortion of brain and cord caused by cervicomedullary football injuries

✓ The problem of serious and fatal football injuries involving the cervicomedullary junction is presented. The mechanisms of such injuries (“stick blocking,” “spearing”) have been analyzed with the help of motion pictures of the action. The second cervical segment of the spinal cord was the commonest site of pathological change. A poor collateral vascular supply to the vertebrobasilar region, compression of the venous sinus, and the great disparity between the distortion of the freely mobile brain and the relatively fixed cervical spinal cord were implicated as the most likely background for the damage, which in turn may lead to acute cerebral edema and tentorial or tonsilar herniation.

Warbled tone masking in bone-conduction audiometry

Warbled tones are compared with narrow-band, wide-band, and complex noises with respect to their efficacy as air-conducted maskers. Bone-conducted pulsed tones of 500, 1000, 2000, and 4000 Hz were presented to the foreheads of eight normal-hearing subjects. With each masker presented binaurally and held constant at a nominal 40-dB level (re normal threshold for each noise) the results indicated that the effectiveness of the warbled tone was essentially comparable to that of the narrowband noise and was significantly better than the wide-band and complex noises over all frequencies combined. Some variation in efficacy was noted, however, as a function of individual frequencies. These results, plus those of the inter- and intra-subject reliabilities and the relative variabilities of the obtained masked thresholds, indicated that a warbled tone may have potential clinical usefulness as a masker.