RESUMO
BACKGROUND: A 24-year-old woman with symptoms of chronic, recurrent headache, presumably secondary to migrainous etiology, came to our clinic and was found to have a congenital retinal macrovessel encircling an area superior to (but not passing through) the macula. CONCLUSIONS: Congenital retinal macrovessels are rare, aberrantly large branches of retinal arteries or veins that typically cross the horizontal raphe to either supply or drain the macular area. These unusual vascular entities must be distinguished from prepapillary vascular loops, racemose hemangiomas, Wyburn-Mason syndrome, or other arteriovenous malformations with potential neuro-ocular sequelae.
Assuntos
Anormalidades do Olho/diagnóstico , Vasos Retinianos/anormalidades , Adulto , Diagnóstico Diferencial , Feminino , Humanos , Acuidade VisualRESUMO
Ten acquisition curves were obtained from each of 4 pigeons in a two-choice discrete-trial procedure. In each of these 10 conditions, the two response keys initially had equal probabilities of reinforcement, and subjects' choice responses were about equally divided between the two keys. Then the reinforcement probabilities were changed so that one key had a higher probability of reinforcement (the left key in half of the conditions and the right key in the other half), and in nearly every case the subjects developed a preference for this key. The rate of acquisition of preference for this key was faster when the ratio of the two reinforcement probabilities was higher. For instance, acquisition of preference was faster in conditions with reinforcement probabilities of .12 and .02 than in conditions with reinforcement probabilities of .40 and .30, even though the pairs of probabilities differed by .10 in both cases. These results were used to evaluate the predictions of some theories of transitional behavior in choice situations. A trial-by-trial analysis of individual responses and reinforcers suggested that reinforcement had both short-term and long-term effects on choice. The short-term effect was an increased probability of returning to the same key on the one or two trials following a reinforcer. The long-term effect was a gradual increase in the proportion of responses on the key with the higher probability of reinforcement, an increase that usually continued for several hundred trials.
