Variation, repetition, and choice

Experiment 1 investigated the controlling properties of variability contingencies on choice between repeated and variable responding. Pigeons were exposed to concurrent-chains schedules with two alternatives. In the REPEAT alternative, reinforcers in the terminal link depended on a single sequence of four responses. In the VARY alternative, a response sequence in the terminal link was reinforced only if it differed from the n previous sequences (lag criterion). The REPEAT contingency generated low, constant levels of sequence variation whereas the VARY contingency produced levels of sequence variation that increased with the lag criterion. Preference for the REPEAT alternative tended to increase directly with the degree of variation required for reinforcement. Experiment 2 examined the potential confounding effects in Experiment 1 of immediacy of reinforcement by yoking the interreinforcer intervals in the REPEAT alternative to those in the VARY alternative. Again, preference for REPEAT was a function of the lag criterion. Choice between varying and repeating behavior is discussed with respect to obtained behavioral variability, probability of reinforcement, delay of reinforcement, and switching within a sequence.     

Perceived reachability in hemispace

A common observation in studies of perceived (imagined) compared to actual movement in a reaching paradigm is the tendency to overestimate. Of the studies noted, reaching tasks have been presented in the general midline range. In the present study, strong right-handers were asked to judge the reachability of visual targets projected onto a table surface at midline, right- (RVF), and left-visual fields (LVF). Midline results support those of previous studies, showing an overestimation bias. In contrast, participants revealed the tendency to underestimate their reachability in RVF and LVF. These findings are discussed from the perspective of actor 'confidence' (a cognitive state) possibly associated with visual information, perceived ability, and perceived task demands.     

Expectations about numerical events in four lemur species (Eulemur fulvus, Eulemur mongoz, Lemur catta and Varecia rubra)

Although much is known about how some primates—in particular, monkeys and apes—represent and enumerate different numbers of objects, very little is known about the numerical abilities of prosimian primates. Here, we explore how four lemur species (Eulemur fulvus, E. mongoz, Lemur catta, and Varecia rubra) represent small numbers of objects. Specifically, we presented lemurs with three expectancy violation looking time experiments aimed at exploring their expectations about a simple 1+1 addition event. In these experiments, we presented subjects with displays in which two lemons were sequentially added behind an occluder and then measured subjects duration of looking to expected and unexpected outcomes. In experiment 1, subjects looked reliably longer at an unexpected outcome of only one object than at an expected outcome of two objects. Similarly, subjects in experiment 2 looked reliably longer at an unexpected outcome of three objects than at an expected outcome of two objects. In experiment 3, subjects looked reliably longer at an unexpected outcome of one object twice the size of the original than at an expected outcome of two objects of the original size. These results suggest that some prosimian primates understand the outcome of simple arithmetic operations. These results are discussed in light of similar findings in human infants and other adult primates.This revised version was published online in March 2005 with corrections to Fig. 6.     

Means-means-end tool choice in cotton-top tamarins (Saguinus oedipus): finding the limits on primates’ knowledge of tools

Most studies of animal tool use require subjects to use one object to gain access to a food reward. In many real world situations, however, animals perform more than one action in sequence to achieve their goals. Of theoretical interest is whether animals have the cognitive capacity to recognize the relationship between consecutive action sequences in which there may be one overall goal and several subgoals. Here we ask if cotton-top tamarins, a species that in captivity uses tools to solve means-end problems, can go one step further and use a sequence of tools (means) to obtain food (end). We first trained subjects to use a pulling tool to obtain a food reward. After this initial training, subjects were presented with problems in which one tool had to be used in combination with a second in order to obtain food. Subjects showed great difficulty when two tools were required to obtain the food reward. Although subjects attended to the connection between the tool and food reward, they ignored the physical connection between the two tools. After training on a two-tool problem, we presented subjects with a series of transfer tests to explore if they would generalize to new types of connections between the tools. Subjects readily transferred to new connections. Our results therefore provide the first evidence to date that tamarins can learn to solve problems involving two tools, but that they do so only with sufficient training.     

‘Core Knowledges’: a dissociation between spatiotemporal knowledge and contact‐mechanics in a non‐human primate?

Human toddlers demonstrate striking failures when searching for hidden objects that interact with other objects, yet successfully locate hidden objects that do not undergo mechanical interactions. This pattern hints at a developmental dissociation between contact-mechanical and spatiotemporal knowledge. Recent studies suggest that adult non-human primates may exhibit a similar dissociation. Here, I provide the first direct test of this dissociation using a search paradigm with adult rhesus monkeys. Subjects watched as a plum rolled behind one of two opaque barriers. In Experiment 1, subjects had to locate the plum based on the position of a wall that blocked the plum's trajectory. Subjects searched incorrectly, apparently neglecting information about the location of the wall. However, subjects searched correctly in Experiments 2-4 when they were given spatiotemporal information about the plum's movement. Results indicate that adult monkeys use spatiotemporal information, but not contact-mechanical information, to locate hidden objects. This dissociation between contact-mechanical and spatiotemporal knowledge is discussed in light of developmental theories of core knowledge and the literature on object-based attention in human adults.     

Exploring the structure of Zuckerman's Sensation Seeking Scale, Form V in a Spanish sample

The psychometric properties of the original version of the Sensation Seeking Scale (Form V) were analyzed in a sample of 1,006 Spanish university students. The total sample was randomly split into two halves. Exploratory factor analyses were conducted on the calibration sample (n=504), whereas confirmatory factor analysis procedures were performed on the validation sample (n=502). As previous studies have suggested, exploratory factor structure indicated that several items load on a different factor or have loadings lower than .30. Those problems were surpassed when the best five items per factor were factor analyzed again. The confirmatory factor analyses showed that a 4-factor simple structure model gave a clearly imperfect fit. A model of 20 items (5 items per factor) gave a better fit, although with similar problems regarding the low reliabilities of the Experience Seeking and Boredom Susceptibility subscales. The need for improvement of the four-factor structure is discussed.     

Degree of illiteracy and phonological and metaphonological skills in unschooled adults

Phonological and metaphonological skills are explored in 97 Brazilian illiterate and semiliterate adults. A simple letter- and word-reading task was used to define the degree of illiteracy. Phonemic awareness was strongly dependent on the level of letter and word reading ability. Phonological memory was very low in illiterates and unrelated to letter knowledge. Rhyme identification was relatively preserved in illiterates and semiliterates, and unrelated to letter and word reading level. Phonetic discrimination (minimal pairs) was fairly good and marginally related to reading ability. These results suggest that phonological sensitivity, phonological memory, rhyme identification, and phonemic awareness are distinctive cognitive processes, and that only phonemic awareness is clearly and strongly dependent on the alphabetical acquisition.