Abstract: Isoluminant stimulus is an image whose edges are defined only by a change in color, not by change in brightness. The stimulus here is imperfect: the blue parts and the green parts of the image are only as nearly equal in brightness as they can be on the printed page. Moreover, the change in brightness beyond the edge of the page is apparent, and so is the fact that the reader is holding the magazine at reading distance. When such cues are removed under laboratory conditions, subjects faced with an isoluminant stimulus prove unable to bring its edges into focus. This deficiency contributes to making a familiar face hard to recognize. The experiment indicates that the brain process underlying visual accommodation (the focusing of the eyes) cannot “see” color; it is a hidden process distinct from the processes that lead to perception. The image shows Groucho Marx as he appeared in the motion picture Horse Feathers.

Abstract: Blood was collected every 3 days for 13 months from 4 captured [female][female] of proven fertility kept adjacent to a teaser stallion. Basal plasma LH level was greater during Apr.-July (8.1+or-0.5 ng/ml) than during Nov.-Jan. (2.2+or-0.2). A total for 21 LH peaks occurred between 13 Apr. and 31 Aug. among the 4 [female][female]; many peaks exceeded 20 times the basal level, and there was a trend to a higher LH level with each succeeding peak. On all occasions except one, LH peaks were associated with progesterone levels of 0.5 ng/ml and with increases of oestrogen (peak average 43.1+or-12.1 pg/ml). Basal progesterone level during Apr.-July (1.5+or-1.2 ng/ml) did not differ significantly from that during Oct.-Jan. (1.1+or-0.7), nor did basal oestrogen level differ significantly between those 2 periods (8.4+or-3.2 and 12.9+or-4.6 pg/ml resp.). Behavioural oestrus always occurred with LH and oestrogen peaks during Apr.-July. However, behavioural oestrus was occasionally observed during Aug.-Oct., when LH peaks no longer occurred.

Abstract: In most cases, the social organisation of each of the seven species of Equidae existing today outside captivity is either territorial or non-territorial. The striking differences found between these two types of organisation in the social grouping and bonds, mating behaviour, leadership and dominance hierarchies of the animals are examined. It is thought that the non-territorial species show a less primitive type of organisation than the territorial animals. Infant Equidae are precocious animals and are able to follow their dams soon after birth. They stay close by their dams and travel with the herd from an early age and are therefore classified as “followers”, in contrast to the species which have a period of hiding after birth. Dams recognise their foals immediately after birth, whereas it takes 2 or 3 days for a foal to form an attachment to its dam. Being in close proximity to their dams, foals are able to nurse frequently and, unless artificially weaned, a foal will nurse until its dam foals again. Foals start to graze during their first week and as they grow older they spend more time grazing and less time nursing and resting. It is normal for foals to be corprophagic until one month old, and this provides them with bacteria essential for the digestion of fibre. Play behaviour is solitary in very young foals, but after 4 weeks of age, foals play together, with male foals playing more than females and showing more aggressive, fighting movements in play.