Unilateral olfactory conditioning in 6-day-old rat pups

The potential that early olfactory learning might be laterally organized in the brain was investigated in 6-day-old rats. This hypothesis is based on the finding that the commissural systems that subserve bilateral olfactory communication do not mature until the second week of postnatal life. Pups were trained with pairings of cedar odor and intraoral infusions of milk while one nostril was occluded. Animals expressed a conditioned orientation towards cedar if tested with the trained nostril open. No such conditioning was observed if the untrained nostril was open during testing. Further, when individual pups received cedar odor/milk pairings with one nostril open and orange odor/milk pairings with the other open, they expressed a conditioned preference for orange when tested with the orange-trained nostril open, and a preference for cedar when tested with the cedar-trained nostril open. Classically conditioned oral responses (mouthing) also appeared to be lateralized. However, no such unilateral conditioning occurred with respect to behavioral activation, which is also conditioned in this paradigm. Increases in activity to the odor CS were observed regardless of whether the trained or untrained nostril was open during testing. These results suggest that in developing rodents, olfactory memories may be partly represented in structures that can be unilaterally accessed during training and testing. They provide a starting point for isolation of neural substrates of the olfactory conditioning process.     

Facial aging, attractiveness, and distinctiveness.

A standard facial caricature algorithm has been applied to a three-dimensional (3-D) representation of human heads, those of Caucasian male and female young adults. Observers viewed unfamiliar faces at four levels of caricature--anticaricature, veridical, moderate caricature, and extreme caricature--and made ratings of attractiveness and distinctiveness (experiment 1) or learned to identify them (experiment 2). There were linear increases in perceived distinctiveness and linear decreases in perceived attractiveness as the degree of facial caricature (Euclidean distance from the average face in 3-D-grounded face space) increased. Observers learned to identify faces presented at either level of positive caricature more efficiently than they did with either uncaricatured or anticaricatured faces. Using the same faces, 3-D representation, and caricature levels, O'Toole, Vetter, Volz, and Salter (1997, Perception 26 719-732) had shown a linear increase in judgments of face age as a function of degree of caricature. Here it is concluded that older-appearing faces are less attractive, but more distinctive and memorable than younger-appearing faces, those closer to the average face.