Stimulus control of Pavlovian facilitation

Two experiments were conducted using an autoshaping procedure with pigeons to examine whether dimensional stimulus control by a Pavlovian facilitator parallels the control established following operant discrimination training. Facilitation training consisted of the presentation of a black vertical line on a white background as the B stimulus in a feature-positive discrimination in which the A stimulus (white keylight) was followed by grain presentation only if preceded by B. In this way, B facilitates or sets the occasion for pecking at A. Subsequent testing for generalization along the line-orientation dimension produced decremental gradients when the facilitation paradigm incorporated an explicit feature-negative stimulus (B−). These results parallel the decremental control obtained following operant discrimination training and suggest that Pavlovian facilitators and instrumental discriminative stimuli are functionally equivalent.     

Behavioral and pharmacological variables affecting risky choice in rats.

The effects of manipulations of response requirement, intertrial interval (ITI), and psychoactive drugs (ethanol, phencyclidine, and d-amphetamine) on lever choice under concurrent fixed-ratio schedules were investigated in rats. Responding on the "certain' lever produced three 45-mg pellets, whereas responding on the "risky" lever produced either 15 pellets (p = .33) or no pellets (p .67). Rats earned all food during the session, which ended after 12 forced trials and 93 choice trials or 90 min, whichever occurred first. When the response requirement was increased from 1 to 16 and the ITI was 20 s, percentage of risky choice was inversely related to fixed-ratio value. When only a single response was required but the ITI was manipulated between 20 and 120 s (with maximum session duration held constant), percentage of risky choice was directly related to length of the ITI. The effects of the drugs were investigated first at an ITI of 20 s, when risky choice was low for most rats, and then at an ITI of 80 s, when risky choice was higher for most rats. Ethanol usually decreased risky choice. Phencyclidine did not usually affect risky choice when the ITI was 20 s but decreased it in half the rats when the ITI was 80 s. For d-amphetamine, the effects appeared to he related to baseline probability of risky choice; that is, low probabilities were increased and high probabilities were decreased. Although increase in risky choice as a function of the ITI is at variance with previous ITI data, it is consistent with foraging data showing that risk aversion decreases as food availability decreases. The pharmacological manipulations showed that drug effects on risky choice may be influenced by the baseline probability of risky choice, just as drug effects can be a function of baseline response rate.     

Extending Free Pregroups with Lower Bounds

In this paper, we propose an extension of free pregroups with lower bounds on sets of pregroup elements. Pregroup grammars based on such pregroups provide a kind of an algebraic counterpart to universal quantification over type-variables. In particular, we show how our pregroup extensions can be used for pregroup grammars expressing natural-language coordination and extraction.     

Do dogs get the point? A review of dog–human communication ability

In recent years evidence has accumulated demonstrating that dogs are, to a degree, skilful in using human forms of communication, making them stand out in the animal kingdom. Neither man's closest relative, the chimpanzee, nor dog's closest living relative, the wolf, can use human communication as flexibly as the domestic dog. This has led to the hypothesis that dogs’ skills in this domain may be a result of selection pressures during domestication, which have shaped dogs’ skills tremendously. One hypothesis, the so-called by-product hypothesis, suggests that dogs have been selected against fear and aggression and as a by-product this paved the way for the evolution of generally more flexible social cognitive skills, which surpassed those of their ancestor, the wolf. Another hypothesis, the adaptation hypothesis, has claimed that dogs may have been specifically selected for certain tasks for which using human forms of communication was necessary. As of yet, the mechanism underlying dogs’ understanding of human forms of communication is not fully understood. We argue here that understanding the mechanism involved will also shed light on possible evolutionary scenarios. We argue that the evidence to date suggests that dogs’ understanding of human forms of communication may be more specialized than was predicted by some and may be best explained as the result of a special adaptation of dogs to the specific activities humans have used them for.     

The Lambek Calculus Extended with Intuitionistic Propositional Logic

We present sound and complete semantics and a sequent calculus for the Lambek calculus extended with intuitionistic propositional logic.     

Differential effects of makeup on perceived age

Makeup accentuates three youth‐related visual features – skin homogeneity, facial contrast, and facial feature size. By manipulating these visual features, makeup should make faces appear younger. We tested this hypothesis in an experiment in which participants estimated the age of carefully controlled photographs of faces with and without makeup. We found that 40‐ and especially 50‐year‐old women did appear significantly younger when wearing makeup. Contrary to our hypothesis, 30‐year‐old women looked no different in age with or without makeup, while 20‐year‐old women looked older with makeup. Two further studies replicated these results, finding that makeup made middle‐aged women look younger, but made young women look older. Seeking to better understand why makeup makes young women look older, we ran a final study and found evidence that people associate makeup use with adulthood. By activating associations with adulthood, makeup may provide an upward bias on age estimations of women who are not clearly adult. We propose that makeup affects social perceptions through bottom‐up routes, by modifying visual cues such as facial contrast, facial feature size, and skin homogeneity, and also through top‐down routes, by activating social representations and norms associated with makeup use.     

Is it a he or a she? Behavioral and computational approaches to sex categorization

Can people categorize the sex of neonate faces? Our experiment tested the sex categorization of neonate faces by adult participants. We used a set of 120 Caucasian faces (adults and 4-day-old neonates) that were presented just once to a large sample of participants. A computational model of low-level visual processing, based on Gabor filters, was used to explore the relation between spatial-frequency information and sex categorization. The results showed that participants were able to categorize the sex of the faces, but were less accurate with neonate (d' = 0.36, β = –.97) than with adult (d' = 3.02, β = –.93) faces. Moreover, faces were more frequently categorized as boys’ than girls’ faces. The computational model suggests that specific spatial-frequency channels carry most of the useful information for the categorization task. Overall, the findings reveal that subtle differences in neonate facial structure were enough to allow the sex categorization of neonate faces, although accuracy was low in both adults and the computational model of low-level visual processing.     

Joint control strategies and hand trajectories in multijoint pointing movements

The role of timing in the control of multijoint pointing movements was evaluated. Eight subjects performed rapid pointing movements to a variety of target locations. The subject's right arm was strapped to a 2 degrees of freedom manupilandum that permitted shoulder and elbow motion in the horizontal plane. Initial and final position of the hand and magnitude of displacement was varied to determine effects on timing characteristics. Kinematics and kinetics of the shoulder, elbow, and hand were analyzed. The hand paths and velocity profiles observed were consistent with prior reports. Multiple regression analysis of kinematic variables disclosed that timing of joint movement onset was independent of initial and final positions of the hand, but was linearly related to joint displacement: the joint that moved farther started moving first. Using computer simulations to create joint movement onset, times that were different from the observed ones always resulted in hand paths with increased curvatures and loss of the smooth velocity profiles. Secondly, a very stable, linear relationship was observed between peak velocity and displacement at both the elbow and shoulder joints. This relationship was not affected by variations in movement space. We suggest that space-time transformation based on difference in joint displacement is used to regulated timing of joint movement onset. The simulations indicate that this transformation is set to produce smooth velocity profiles. The relationships between timing of movement onset and displacement and between peak velocity and displacement complement each other: by maintaining a linear relationship between velocity and displacement, a linear space time transformation can be used to control timing. Furthermore, these relationships are probably used to simplify coordination between the moving joints.