Perceiving affordances for another person's actions.

The perception of affordances for the actions of other people (actors) was examined. Observers judged the maximum and preferred sitting heights of tall and short actors. Judgments were scaled in centimeters, as a proportion of the observer's leg length, and as a proportion of each actor's leg length. In Experiment 1 observers viewed live actors standing next to a chair. When judgments were scaled by actor leg length, they reflected the actual ordinal relation between the capabilities of the actors. The perception of affordances from kinematic displays was then evaluated. Observers differentiated tall and short actors, but only when the displays contained direct information about relations between the actors and the chair. It is concluded that observers can perceive affordances for the actions of actors and that kinematic displays can be enough to support such percepts if they preserve actor-environment relations that define affordances.

Effect of velocity on judgments of relative mass.

Research indicates that people can accurately judge the relative mass of colliding objects, i.e., which is heavier, if the collisions viewed involve actual physical objects. This study explored whether such judgements are affected by the image velocity of the colliding objects. Videotaped collisions involving different screen velocities were shown to observers. The accuracy of judgments of collision decreased significantly at slower velocities. A velocity-threshold hypothesis is offered as a possible account for this finding.

Noticing of unexpected events by adults with and without mental retardation.

Adults without mental retardation commonly fail to notice nominally obvious aspects of naturalistic scenes (Becklen & Cervone, 1983). We replicated and extended this effect to adults with mild mental retardation. Adults with and without retardation viewed a 60-second videotape of an amateur basketball game. They were instructed to press a button whenever the ball was passed. At one point, a woman carrying an open umbrella walked bodily through the ongoing action. Becklen and Cervone found that only 35% of adults without retardation noticed this unexpected event and that noticing was not predicted by task performance prior to the woman's appearance. In the present study noticing rates for subjects without retardation were similar to those reported by Becklen and Cervone and noticing by subjects with mental retardation was at least as high. Task performance for subjects with mental retardation was significantly lower than that of subjects without retardation, but noticing was not predicted by task performance (prior to the unexpected event) for either group. Results were interpreted in the context of an ecological approach to attention.

A thyromimetic that decreases plasma cholesterol levels without increasing cardiac activity.

A number of agents that mimic the ability of the thyroid hormone, T3, to decrease plasma cholesterol levels are described; one is as effective as T3 at reducing cholesterol levels and stimulating liver function, but has very little effect on cardiac function and is thus less likely to be toxic. The agent may be useful in the treatment of atherosclerosis.

Changes in cardiac function following administration of thyroid hormones in thyroidectomised rats: assessment using the isolated working rat heart preparation.

We investigated the changes in cardiac function following alterations in thyroid state of rats, using the isolated working heart preparation. This technique allows heart rate, contractility, and pump function to be studied under controlled conditions. Surgical thyroidectomy resulted in significant impairment of cardiac function. Single doses of 3,5,3'-triiodo-L-thyronine (T3) or L-thyroxine (T4) were given to thyroidectomised rats. Cardiac function was restored to normal within 48 h of administration of 0.5 mg/kg T3 or 2.5 mg/kg T4 without significant changes in heart weight. The dose-response relationships between T3 and T4 and cardiac function showed that significant changes occurred after single doses of T3, 0.02 mg/kg, or T4, 0.5 mg/kg. An increase in contractility was seen within 12 h of administration of T3, before other physiological effects of T3 are reported to occur. This indicates that the change in contractility is the result of a direct effect of thyroid hormones on the heart and is not secondary to changed loading conditions of the heart. Changes in heart rate occurred between 18 and 48 h. The maximum heart rate achieved did not exceed that in hearts from euthyroid rats, although contractility could be increased above euthyroid levels.

Histamine H1- and H2- receptor antagonists reduce histamine-induced increases in vascular permeability and oedema formation in cat skeletal muscle.

Intra-arterial fusions of histamine cause vasodilation of resistance vessels, extravasation of albumin and oedema in cat skeletal muscle. Treatment with either mepyramine or metiamide significantly reduced the extravasation of albumin and rate of oedema formation. The doses of mepyramine and metiamide used did not modify the vascular responses to bradykinin.

Differentiation of the roles of histamine H1- and H2-receptors in the mediation of the effects of histamine in the isolated working heart of the guinea-pig.

1 Differentiation of the roles of histamine H1- and H2-receptors in the mediation of the effects of histamine on the isolated working heart of the guinea-pig was achieved through the use of histamine and selective histamine receptor agonists and antagonists. 2 Histamine over the dose range 10(-9) mol to 10(-6) mol produced dose-related increases in sinus rate, left intraventricular pressure (LVP)max, LVdP/dtmax, coronary flow, aortic flow, total cardiac output and external pressure-volume work. 3 Dimaprit, a selective histamine H2-receptor agonist, produced very similar responses to histamine. 4 2-Pyridylethylamine, a selective histamine H1-receptor agonist, had little effect on cardiac function unless large doses were administered. Such doses produced increases in all measured parameters. 5 Cimetidine, a selective histamine H2-receptor antagonist, antagonized the effects of histamine and dimaprit and some but not all effects of 2-pyridylethylamine. In the presence of cimetidine a decrease in all parameters with the exception of sinus rate was observed with both histamine and 2-pyridylethylamine. 6 The selective histamine H1-receptor antagonist, mepyramine, had little effect on responses to all three agonists. However, the depressant effects observed with histamine and 2-pyridylethylamine in the presence of cimetidine were antagonized by mepyramine. 7 The results indicate the important role of the histamine H2-receptor in the mediation of the gross cardiac effects of histamine and also indicate that histamine H1-receptors can mediate cardiac depression.

The cardiovascular response to dimaprit, a selective histamine H2-receptor agonist.

1 The cardiovascular responses to dimaprit (S-(3-dimethylaminopropyl) isothiourea) a selective histamine H2-receptor agonist have been studied in anaesthetized cats, dogs, rats and rabbits. 2 Dimaprit lowered systemic arterial blood pressure in all species whether given by intravenous injection or by continous infusion. Intra-arterial injections or infusions caused vasodilatation in the femoral vascular bed. 3 In the cat, continuous intravenous infusions of dimaprit lowered blood pressure without any significant change in heart rate or cardiac output. The fall in blood pressure was thus due to a decrease in peripheral vascular resistance. 4 Dimaprit, given intravenously, increased coronary and gastric blood flows and there were associated marked reductions in vascular resistance. Small reductions in vascular resistance occurred in skeletal muscle, in the intestine and the kidneys. 5 The histamine H2-receptor antagonists, metiamide and cimetidine, antagonized the depressor and vasodilator responses to dimaprit.

The effects of histamine on skeletal muscle vasculature in cats.

1. Experiments have been made to determine the vascular effects of histamine and the mechanism of histamine-induced oedema formation in cat skeletal muscle. 2. Histamine caused dose-dependent dilatation of resistance vessels and increased intravascular volume over the dose range 1 X 10(-10)-1 X 10(-8) mol/kg min. The dilatation of resistance vessels resulted in dose-dependent increases in capillary hydrostatic pressure. 3. Histamine increased vascular permeability, as measured by accumulation of [131I]human serum albumin in the tissue, during infusions at 1 X 10(-8) mol/kg min but no albumin accumulation could be detected at lower infusion rates. 4. Oedema formation during histamine infusion of 1 X 10(-10) and 1 X 10(-9) mol/kg min seemed to be due to increases in capillary hydrostatic pressure and independent of increased vascular permeability. During infusions of histamine 1 X 10(-8) mol/kg min oedema was due predominantly to increased vascular permeability and to a lesser extent, the increase in capillary hydrostatic pressure.

Histamine receptors in peripheral vascular beds in the cat.

1. The vasodilator activity of histamine has been studied in anaesthetized cats. 2. Histamine causes dose-dependent vasodilatation in the vasculature of the hind-limb and mesentery, perfused with blood at constant flow. 3. Experiments using the selective antagonists mepyramine and metiamide indicate the involvement of both H1- and H2-receptors in the vasodilator responses to histamine. Mepyramine (2.5 X 10(-6) mol/kg), causes displacement of the histamine dose-response curve. This displacement is maximum with a dose-ratio of about 10. Further dose-dependent displacement of the dose-response curve occurred after metiamide (4 X 10(-7) mol kg-1 min-1 and 2 X 10(-6) mol kg-1 min-1), although these doses of metiamide had no effect on histamine responses in the absence of mepyramine. 4. Vasodilator responses could also be elicited by the selective H1-receptor agonists, 2-methylhistamine, 2-(2-aminoethyl)pyridine and 2-(2-aminoethyl)thiazole and the selective H2-receptor agonist, 4-methylhistamine. 5. The selectivity of mepyramine and metiamide as histamine receptor antagonists was confirmed by their failure to reduce the vasodilator responses to acetylcholine, isoprenaline and bradykinin.