Contrast sensitivity of the human neonate measured by the visual evoked potential

Visual evoked potentials (VEPs) were recorded from a total of 97 1- to 10-day-old infants, with phase-reversing sinusoidal grating stimuli. The grating contrast or spatial frequency for which 50% of infants gave a statistically significant VEP was taken as a measure of threshold. This procedure yielded an estimate of neonatal acuity of 0.85 cycles/degree and an optimal contrast threshold of 50%. VEPs from an older infant showed good agreement with behavioral measures of sensitivity on the same individual. Comparison of the neonatal VEP results with behavioral data from 5-week-old infants, suggests little change in visual performance over the first month of life.

Infant astigmatism measured by photorefraction

Photorefraction of a sample of 93 infants of ages 1 day to 12 months showed that 63 percent of the subjects had astigmatism of 0.75 diopter or greater, and 12 percent greater than 2 diopters. Seventy percent of these astigmatisms were in the horizontal-vertical meridians. By comparison, only 8 percent of a sample of 26 adults tested by the same method showed astigmatism (all 0.75 to 1 diopter). The high incidence of infant astigmatism has implications for critical periods in human visual development and for infant acuity.

Comparison of effects of quinidine and dihydroquinidine on canine heart

Various cardiac effects of quinidine and dihydroquinidine were tested in isolated dog hearts and in vivo in dogs. No significant differences were found in the negative inotropic, chronotropic, and dromotropic effects. Dihydroquinidine was more potent than quinidine in decreasing coronary arterial pressure.

The dependence of the visual numerosity limit on orientation, colour, and grouping in the stimulus

Visual numerosity judgements were made for tachistoscopically presented arrays of dots. The arrangement within the arrays was either linear or such that dots could be easily perceptually subdivided into two groups. Subdivision was either in terms of an orientation difference, a colour difference, or a spacing difference in the centre of the array. For a large difference in orientation between the two 'arms' of the array (90 degrees), or a large central space (three times the interdot interval) up to 8 dots were accurately perceived. This numerosity limit was twice that found for equivalent linear arrays, with no grouping. Although in terms of accuracy it seems that in these conditions the two groups within each array can be counted independently, there is no evidence for independent processing in terms of response times. From the results of a subsidiary experiment it seems likely that the slow response times in the subgrouping conditions are due to the necessity of processes other than counting (such as judgements of symmetry). For arrays where subgrouping was in teems of a colour difference, or an orientation difference of between approximately 45 degrees and 90 degrees, or a small central space of twice the interdot interval, there was an improvement in accuracy compared to equivalent linear arrays, but no evidence of independent processing, up to a limit of 4, in each of the subgroups. From these preliminary results, tentative proposals concerning 'numerosity' units and their properties are made.

The magic number 4 +/- 0: a new look at visual numerosity judgements

Visual numerosity judgements were made for tachistoscopically presented linear arrays of dots or lines. The interelement interval (which could be specified in spatial frequency terms) was constant for a given array but varied across conditions. A clear limit in the accuracy of numerosity judgements was found to be set at 4 for regularly spaced elements with spatial frequencies below approximately 10 cycles/deg (element and interelement interval of 0-05 deg). This limit in terms of accuracy is accompanied by a fast and almost constant response time for arrays of 4 or less, compared to response times for arrays of more than 4 elements. The limit in accuracy falls to 2 elements rather than 4 for spacing narrower than 0-05 deg alghough with such spacing the elements are still easily resolved. The limit of 4 is found if the stimulus is a bright afterimage, lasting for approximately 60 s. This result suggests that the limit is independent of the time allowed for a single fixation and is a perceptual limit rather than a limit in some memory buffer. 'Numerosity' units are propsoed to account for the results.

[The effect of coffee and coffee components on the stomach muscle]

The isolated stomach muscle strip preparation works well when given pure compounds which are stable and non-toxic. When complex test mixtures such as coffee are used, however, the results are more difficult to interpret. This is probably due to non-specific effects of such mixtures, e.g. induction of changes in organ bath pH, etc. In spite of the above remark, differences in the effects of decaffeinated and normal instant coffees were clearly seen. The so-called "wholesome" coffees gave results identical to those obtained with normal instant coffee. In general, coffee induced muscle contraction followed by relaxation. Choline (possibly together with potassium) would appear to be responsible for the contractions observed, and caffeine for the relaxation.

Steroscopic discrimination in infants

The ability to make discrimiations of binocular disparity was investigated in 2-month-old infnats by two methods: (a)fixation preference between patterns differing in the disparity they contained, and (b)recovery from habituation of high-amplitude sucking when there was a change in disparity in the visual reinforcer. The stimuli were random-dot steregrams. The results for both mthods indicated that at least some infants of this age could perform steroscopic discriminations and that both techniques were feasible for development for longitudinal studies of steroscopic vision.

An automatic device for the isolated rabbit heart preparation for testing cardioactive drugs

An automatic device for the isolated rabbit heart is described. Test solutions are perfused from reservoirs via valves, the sequence and time of opening of which is controlled by a programmable unit. The perfusate was pushed through the heart at a constant flow-rate, with pressure measurement serving as an indicator of preparation stability. The system worked well giving reproducible results without tedious, repetitive manual work. The results obtained with caffeine were in line with those reported in the literature, there being a dose-dependent increase in rate and force of contraction.

The effect of caffeine on barbiturate sleeping time and brain level

The effect of caffeine and coffee on the sleeping time induced by barbital was tested in rats. It was found that caffeine pretreatment shortened barbital-induced sleeping time and that coffee had an effect in direct proportion to its caffeine content; decaffeinated coffee was without effect. It was hypothesized that the shortening was due to an interaction at the brain level. This hypothesis was tested using hexobarbital which is metabolized by the liver whereas barbital is only negligibly so metabolized. Pretreatment with caffeine was found to shorten the hexobarbital sleeping time even though the brain concentration of the latter was actually elevated. It was also shown that caffeine pretreatment was much less effective than phenobarbital pretreatment in stimulating the enzyme systems in the liver which metabolize hexobarbital, aminopyrine and ethylmorphine (in vitro). Consequently, it is concluded that caffeine stimulation of liver metabolism is a relatively minor factor in the shortening of barbiturate sleeping time by caffeine in comparison to the brain interaction of these two drugs.

A quantitative study of the anticholinergic action of several tricyclic antidepressants on the rat isolated fundal strip

1. Investigations were carried out on the antagonism of the action of carbamylcholine chloride on the isolated fundus of the rat stomach by several tricyclic antidepressants.2. The anticholinergic potency of the compounds was in the order: GP 45437>amitriptyline>protriptyline>desmethylimipramine>opipramol. All of the antagonists were less effective than atropine.3. Statistical analysis was carried out to determine whether the theory of competitive antagonism would fit the data obtained.

The effect of available dietary zinc on the utilization of protein by the chick and Japanese quail

1. Chicks and quail (Coturnix japonica) were used in the measurement of net protein utilization and true digestibility of nitrogen of isolated soya-bean protein and a mixture of casein and gelatin in zinc-deficient diets.

2. The net protein utilization values for both protein sources were increased when the diets were supplemented with Zn or with the disodium salt of ethylenediaminetetra-acetic acid, as was the true digestibility of nitrogen of the isolated soya-bean protein.

The influence of infection on titres of antiglobulin antibodies

The influence of acute and chronic infection and hypergammaglobulinaemia on the titres of anti-globulin antibodies was studied in 128 patients. Very high titres of serum agglutinators were found to be associated with gram positive septicaemia. This infection had no influence on the titres of rheumatoid factors. Elevated titres of serum agglutinators may be helpful in differentiating `benign' from `malignant' gammopathy.

Mikulicz's Disease

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