A comparison of monocular and binocular depth perception in 5- and 7-month-old infants

Monocular depth perception was compared with binocular depth perception in 5- and 7-month-old infants. Reaching was used as the dependent measure. Two objects, identical except in size, were presented simultaneously to each infant. The smaller object was within reach for the infants while the larger object was just beyond reach. The two objects subtended equal visual angles from the infants' observation point. With binocular presentation, 96% of the 7-month-olds' reaches and 89% of the 5-month-olds' reaches were for the nearer object. With monocular presentation, 58% of the 7-month-olds' reaches and 65% of the 5-month-olds' reaches were for the nearer object. The reaching preferences observed in the monocular condition indicated sensitivity to monocular depth information (motion parallax, accommodation, and relative size information were available). Binocular viewing, however, resulted in a far more consistent tendency to reach for the nearer object. This result suggests that the infants' perception of the objects' distances was more veridical in the binocular condition than in the monocular condition.     

The role of self-produced movement and visual tracking in infant spatial orientation

In two longitudinal studies, infants were trained at 12 and 18 months to find an object hidden in one of two identical wells in a Plexiglas box. On the test trial, normal access was blocked and infants were either guided by their mother or allowed to move on their own to another opening on the opposite side. In Experiment 1 significantly more correct responding occurred after active movement than after passive at 12 months, with correct responding related to high visual tracking. In contrast, at 18 months correct search without tracking predominated among both movement conditions. A difference between the conditions in the position of the mother on the test trial was ruled out as a contributor to performance on the basis of data from Experiment 2. When opaque sides were inserted to prevent tracking in Experiment 3, active movement no longer facilitated correct search at 12 months, thus indicating that the tracking and not the active movement per se was the critical factor.     

The selective impact of question form and input mode on the symbolic distance effect in children

Five experiments are reported on the symbolic distance effect (SDE) and related phenomena with 6- and 9-year-old children. In the first of these, children were asked to judge the relative sizes of animals in verbal and pictorial tests featuring the comparatives "bigger" and "smaller." A perceptual condition with actual objects was included by way of comparison. A Symbolic Distance Effect was obtained for both lexical and pictorial input. Mode differences were also observed. Pictures produced faster responses than words, and congruity effects occurred only in the pictorial condition. Although performance was similar in tests with either comparative, our subsequent experiments on both 6- and 9-year-olds reveal a significant asymmetry in the child's capacity to verify statements of relation as a function of the direction along the (size) continuum implied by the question. However, important differences between age groups also apparent in the data lead us to conclude that the older subjects develop strategies to overcome this asymmetry by translating certain statements of relation into a form more congruent with their natural modes of encoding.     

The effect of television-mediated aggression and real-life aggression on the behavior of Lebanese children

This study investigated the effect of television-mediated aggression and real-life aggression on the behavior of Lebanese children. The sample consisted of 48 boys and 48 girls of Lebanese origin who were students in an elementary school in Beirut, Lebanon. After controlling for pre-experimental aggression, the subjects were randomly assigned to one of the following treatment conditions: human-film aggression, cartoon-film aggression, neutral film, or real-life (act of war) aggression. The results indicated that boys as a group were more aggressive than girls and exhibited more imitative aggression after viewing both violent film and real-life violence. Girls were not more violent after viewing filmed aggression but were affected by the real-life violence. Comparisons of Bandura's work within the Lebanese culture are made.     

Food anticipation and lever-directed activities in rats

Three experiments are described which elaborate some of the conditions under which rats will contact and manipulate a periodically presented retractable lever. Experiment 1 demonstrated that (i) initial manipulative oral and manual contact with the lever was facilitated if the rat had previous experience of food delivery in the experimental chamber; (ii) persistence in contacting the lever on successive presentations was a function of whether food continued to be presented in the experimental environment; and (iii) food satiation significantly reduced the tendency of the rat to contact the lever even though an expectancy of food had previously been established under conditions of food deprivation. Experiment 2 suggested that the tendency to approach and contact the lever was in part a function of the local moment-to-moment conditional probability of food delivery. Experiment 3 found that the probability of contacting the lever was higher during presentation of an auditory CS signaling a high rate of food delivery than during stimuli signaling no food at all. These results are interpreted as suggesting that the food-signaling aspects of an appetitive CS and that CS's ability to generate signal-directed behaviors are experimentall separable properties.     

Selective association learning in the rat: Generality of response system

Three experiments with rats examined the possibility that the cue-consequence specificity effect is not mediated by the conditioning of selective associations, but instead reflects the selective behavioral expression of taste-illness and exteroceptive-shock conditioning. Experiment 1 showed that the selective aversion performance could be obtained despite the use of locomotor withdrawal from the CS as the index of conditioning. Experiment 2 compared the response profiles of animals conditioned with footshock or illness to presentation of a saccharin or noise CS. During the test with the noise CS, lithium-conditioned subjects did not differ from control rats on any of several behavioral categories, but shock-conditioned rats showed high levels of freezing in response to the noise cue. During the saccharin test, lithium-treated rats engaged in behaviors such as chin wiping, head shaking, and gaping; these behaviors were rarely or never seen in shock-conditioned rats or controls, whose behavioral profiles during the saccharin test were almost identical. Experiment 3, using a blocking design, found that a noise-lithium pairing did not attenuate subsequent conditioning of a saline-lithium association, nor did a saccharin-shock pairing interfere with conditioning of a noise-shock association. These results confirm that the cue-consequence specificity effect is mediated by the selective associability of taste with illness and of exteroceptive cues with footshock.     

Mechanisms of blocking by contextual stimuli

The influence of contextual stimuli on the conditioning and performance of responding to a discrete stimulus was examined in the US preexposure paradigm using both context shift manipulations and a measure of context conditioning. Four groups of rats received both repeated exposure to an electric shock US in one context (Context 1), and repeated nonshocked exposure to a second context (Context 2). Two additional groups of rats received exposure to these contexts, but never received shock presentations. Rats exposed to shock learned to escape from the stimuli of Context 1, but did not escape from the stimuli provided by Context 2. Rats not exposed to shock failed to escape from either context. All rats then received a single CER conditioning session in which four pairings of a 3-min noise CS and shock US were presented. Half the rats received those CS-US pairings in the excitatory Context 1, while the remaining rats received those pairings in the neutral Context 2. Finally, half the rats in each of the CER conditioning treatments received extinction test trials of the noise CS in Context 1, while the remaining rats received those test trials in Context 2. Thus, this design factorially manipulated the presence of excitatory or neutral contextual stimuli during both conditioning and testing of a discrete CS. In comparison with the two groups of rats never preexposed to shock alone, attenuation in acquisition of conditioned suppression observed during test trials occurred only when CER conditioning had been administered in the excitatory Context 1, and this effect was manifested when testing occurred in either the excitatory Context 1 or the neutral Context 2. These results support the model of R. A. Rescorla and A. R. Wagner (1972) (in A. H. Black & W. F. Prokasy (Eds.) Classical Conditioning II, pp. 64–99, New York: Appleton-Century-Crofts) which asserts that contextual stimuli and sicrete CSs compete for limited associative strength supportable by a given US.     

Feedback during exposure to inescapable shocks and subsequent shock-escape performance

In two experiments, we assessed the ability of a feedback stimulus during helplessness training to reduce the performance deficits common to inescapable shock. In each experiment, four groups of rats were exposed to either escapable shock (E), inescapable shock with a feedback stimulus following shock termination (Y-FS), inescapable shock with no feedback stimulus (Y-NFS), or no shock (N). The feedback stimulus eliminated the interference effects of inescapable shock when tested with an FR-3 lever press escape task (Experiment 1) or on an FR-1 task with a 3-s delay between the response and shock termination (Experiment 2). These results suggest that stress-induced biochemical changes may mediate the interference effects seen in inescapably shocked rats.