Open-ended categorization of chick-a-dee calls by black-capped chickadees (Poecile atricapilla)

The authors trained black-capped chickadees (Poecile atricapilla) in an operant discrimination with exemplars of black-capped and Carolina chick-a-dee calls, with the goal of determining whether the birds memorized the calls of conspecifics and heterospecifics or classified the calls by species. Black-capped calls served as both rewarded (S+) and unrewarded (S-) stimuli (the within-category discrimination), whereas Carolina chick-a-dee calls served as S-s (the between-category discrimination) in the black-capped chick-a-dee call S+ group. The Carolina call S+ group had Carolina calls as S+s and S-s (within-category) and black-capped calls as S-s (between-category). Both groups discriminated between call categories faster than within a call category. In 2 subsequent experiments, both S+ groups showed transfer to novel calls and propagation back to between-category calls. The results favor the hypothesis that the acoustically similar social calls of the 2 species constitute separate open-ended categories.     

The effects of hypothermia and hunger on the duration of bar pressing for intracranial self-stimulation in rats

Hypothermic rats at rectal temperatures below 30° C showed decreased duration of bar pressing for intracranial self-stimulation in lateral hypothalamic sites. The same effect was found in hungry rats. Both with cooling and hunger, decreased durations were accompanied by decreased thresholds. The threshold changes in hypothermic rats exceeded 12 μA in some cases. The results are relevant to explanations of why animals turn off rewarding brain stimulation. Particular attention is given to the possibility that cooling enhances neural activity in facilitatory connections between positive and aversive systems.     

A peak shift on a line-tilt continuum

Pigeons were trained to discriminate the presence or absence of a vertical line, and their performance on a subsequent generalization test was compared with that of other pigeons trained to discriminate a vertical from a 45° line. On the generalization gradient after discrimination training, the presence/absence discrimination group showed a peak at 0° (vertical) while the peak for the 0°/45° discrimination group shifted from 0° in a direction away from the 45° line. The results, discussed in connection with a recent suggestion about the role of color in the peak-shift effect, are interpreted as supporting the generality of the phenomenon.     

Do children learn the integers by induction?

According to one theory about how children learn the meaning of the words for the positive integers, they first learn that "one," "two," and "three" stand for appropriately sized sets. They then conclude by inductive inference that the next numeral in the count sequence denotes the size of sets containing one more object than the size denoted by the preceding numeral. We have previously argued, however, that the conclusion of this Induction does not distinguish the standard meaning of the integers from nonstandard meanings in which, for example, "ten" could mean set sizes of 10, 20, 30,... elements. Margolis and Laurence [Margolis, E., & Laurence, S. (2008). How to learn the natural numbers: Inductive inference and the acquisition of number concepts. Cognition, 106, 924-939] believe that our argument depends on attributing to children "radically indeterminate" concepts. We show, first, that our conclusion is compatible with perfectly determinate meanings for "one" through "three." Second, although the inductive inference is indeed indeterminate - which is why it is consistent with nonstandard meanings - making it determinate presupposes the constraints that the inference is supposed to produce.     

THE HARM OF IMMORALITY

A central problem in moral theory is how it is to be defended against those who think that there is no harm in being immoral, and that immorality can be in one's self‐interest, assuming the perpetrator is not caught and punished. The argument presented here defends the idea that being immoral prevents one from having self‐respect. If it makes sense to think that one cannot be happy without self‐respect, then the conclusion follows that one cannot be both immoral and happy. Immorality is harmful because its self‐disrespecting nature keeps immoralists from being happy. This is the harm of immorality.     

Explaining outcome type interactions with frame: Aspiration level and the value function

Research on framing effects has revealed cases where the type of outcome at risk (e.g., human lives vs. animal lives) affects the magnitude of the framing effect. Some authors have appealed to the shape of the value function as predicting when framing effects will occur: The more valuable the outcome type, the more nonlinear its value function, and the larger the resulting framing effect (Levin & Chapman, 1990). However, having a more or less nonlinear value function cannot explain situations in which participants strongly prefer the same option in both frames. Another factor that may be at work in these types of outcome effects is an aspiration level (AL; Lopes, 1987; Schneider, 1992), which determines how acceptable the options are and combines (or competes) with the risk attitude encouraged by frame. The results described here indicate that differences in the shape of the value function between outcome types are evident but are inconsistent between framed losses and gains, though nonlinearity in the value function can be increased with a manipulation that also encourages framing effects. The results also demonstrate that an AL can lead to the same predominant risk preference in the positive and negative frame. These findings indicate that the shape of the value function and the AL each play a role in outcome type interactions with frame, and in some cases, a combination of the two factors may be at work.     

Some temporal properties of behavioral contrast

Pigeons were rewarded on a variable time interval for pecking a translucent key illuminated with either a 45 degrees or a vertical line. The key illumination changed every 2 min during daily 1-hr sessions. When the rates of pecking were stable, reinforcement was omitted in the presence of the 45 degrees line. Responding in the presence of the vertical line increased. This increase did not disappear when responses to the 45 degrees line were once more reinforced, but when reinforcements for responses in the presence of the 45 degrees line were again omitted, responding to the vertical line increased again. After the second alternation of these two procedures, the increased responding to the vertical line appeared when responses were not reinforced in the presence of the 45 degrees line, and disappeared when reinforcement was available during both stimuli. In a second experiment, the key illumination changed between sessions only, so that 1-hr sessions of reinforcement and non-reinforcement occurred on alternate days. Responding to the vertical line still increased when responding to the 45 degrees line was not reinforced, but the increase tended to disappear during the session.     

Behavioral contrast and relative reinforcement frequency in two multiple schedules

After preliminary variable-interval training, one group of pigeons was trained on a series of multiple variable-interval low-rate reinforcement schedules, while another group was trained on a series of multiple variable-interval fixed-ratio reinforcement schedules. Contrast effects were observed as variable-interval baseline rate changed in a direction away from the change in reinforcement frequency in the other component. The effects of the variable-interval component on performance in the low-rate and fixed-ratio reinforcement components in the multiple schedules were assessed by comparing the birds' performances on each of these schedules alone. Fixed-ratio reinforcement schedules showed a susceptibility to contrast effects, low-rate reinforcement schedules did not. The rate of reinforcement in fixed-ratio schedules at which no interaction occurred in the multiple schedules was higher than that in variable-interval 1-min schedules, suggesting that pigeons may prefer time-based, rather than response-based, reinforcement.