Squirrel monkeys (Saimiri sciureus) choose smaller food arrays: long-term retention, choice with nonpreferred food, and transposition

Squirrel monkeys (Saimiri sciureus) that had learned to reach toward 1 piece of food instead of 4 in a reverse-reward contingency were tested after an 8-month delay with no intervening relevant experiences. All monkeys except 1 continued to show inhibitory control by reliably reaching toward the smaller quantity, most of them doing so within 2 sessions. Performance was maintained when a low-preference food replaced prized foods as arrays and rewards. When the quantities 1 and 4 were replaced with different ones, there was strong evidence of transposition at group level, although individual differences in bias toward the smaller quantities became apparent. Individual differences in mastering the original task more than 8 months previously were quite stable, suggesting robustness in the operations required for this form of self-control.     

Differential effects of physical and psychological stressors on immune functions of rats

To study the effects of different types or durations of stressors on immune functions, male Fischer rats were exposed to chronic physical (electric foot shock) or psychological (non-foot shock) stress induced in the communication box. Superoxide production by alveolar macrophages (AMs), mitogen-induced splenic lymphocyte proliferation, and splenic natural killer (NK) cell cytolysis were examined in vitro. Repeated exposure to physical stress suppressed superoxide production by AMs (-58%, p<0.05 for opsonized zymosan (OZ) and -51%, p<0.05 for phorbol 12-myristate 13-acetate (PMA)), although psychological stress suppressed superoxide production after 24 h of repeated exposures (-40%, p<0.05 for OZ and -47%, p<0.05 for PMA). Acute suppression of the blastic response of splenic lymphocytes was only found in the physical stress group (p<0.05), although the chronic effects were only found in the psychological stress group (p<0.05). NK cell activity was suppressed immediately after the acute physical stress (-30%, p<0.05), but no effects were found in the psychological stress group. These results underline the importance of distinguishing between physical versus psychological stressors when examining the effects of stress on immune functions.     

Surreptitiously projecting different movies to two subsets of viewers

A new technique (manipulation of overlapping rivalrous images by polarizing filters, or MORI) has been invented for presenting on the same screen two different images that can be seen separately by two groups of viewers without their noticing the overlap. It can easily create desired artificial conflicts among viewers. Two perpendicular polarizing filters provide separate invisible channels from dual video projectors to two groups of viewers on a single screen. The basic principle of the presentation technique, details of the apparatus, and limitations are introduced. As an example of the application of this technique, an eyewitness experiment is briefly reported. The results of experiments conducted by the author and colleagues provide evidence of the effectiveness of this technique with various projectors, video materials, group sizes, and ages of participants.     

Pigeons (Columba livia) integrate visual motion using the vector average rule: effect of viewing distance

Animal Cognition - Integrating local motion signals detected by the primary motion detector is crucial for representing a rigid, two-dimensional motion. The nature of motion integration has been...     

Understanding of the relationship between seeing and knowing by tufted capuchin monkeys (Cebus apella)

The ability of four tufted capuchin monkeys (Cebus apella) to recognize the causal connection between seeing and knowing was investigated. The subjects were trained to follow a suggestion about the location of hidden food provided by a trainer who knew where the food was (the knower) in preference to a trainer who did not (the guesser). The experimenter baited one of three opaque containers behind a cardboard screen so that the subjects could not see which of the containers hid the reward. In experiment 1, the knower appeared first in front of the apparatus and looked into each container; next, the guesser appeared but did not look into any containers. Then the knower touched the correct cup while the guesser touched one of the three randomly. The capuchin monkeys gradually learned to reach toward the cup that the knower suggested. In experiment 2, the subjects adapted to a novel variant of the task, in which the guesser touched but did not look into any of the containers. In experiment 3, the monkeys adapted again when the knower and the guesser appeared in a random order. These results suggest that capuchin monkeys can learn to recognize the relationship between seeing and knowing. Accepted after revision: 10 September 2001 Electronic Publication     

Observing emotion in infants: facial expression,body behavior,and rater judgments of responses to an expectancy-violating event

Eleven-month-old European-American, Japanese, and Chinese infants (ns = 23, 21, and 15, respectively) were videotaped during baseline and stimulus episodes of a covert toy-switch procedure. Infants looked longer at the object during the expectancy-violating event (stimulus episode) but did not produce more surprise-related facial expressions. American and Japanese infants produced more bodily stilling during stimulus than baseline, and American infants also produced more facial sobering. Naive raters viewing both episodes could correctly identify the expectancy-violating event. Rater judgments of surprise were significantly related to infants' bodily stilling and facial sobering. Judgments of interest were related to cessation of fussing. Thus, observer judgments of infant emotions can be systematically related to behaviors other than prototypic emotional facial expressions.     

Perceptual completion in rhesus monkeys (Macaca mulatta) and pigeons (Columba livia)

In a two-dimensional drawing, when the narrow edge of a bar appears to touch the edge of a large rectangle, humans overestimate the length of the bar (Kanizsa, 1979). Kanizsa has suggested that this illusion occurs because humans perceive the bar as continuing behind the rectangle and complete the “occluded” portion of the bar. Rhesus monkeys and pigeons were trained to classify black target bars with a variety of lengths as “long” or “short.” In training, the bar was always located at the same distance from a gray box. After learning this discrimination, the subjects were tested on novel stimuli, in which the bar was located at three new locations. Monkeys showed a consistent response bias for “long” when the bar touched the box, but pigeons did not. Monkeys appear to have completed the “occluded” part like humans, whereas pigeons failed to do so. Because this procedure does not require animals to complete the “occluded” part with any particular form, their failure suggests that pigeons do not even perceive the target bar as continuing behind the “occluding” figure. The failure of pigeons may be due to difficulty in perceiving depth from two-dimensional drawings.     

Left-side dominance for song discrimination in Bengalese finches (Lonchura striata var. domestica)

Male Bengalese finches are left-side dominant for the motor control of song in the sensorimotor nucleus (the high vocal center, or HVc) of the telencephalon. We examined whether perceptual discrimination of songs might also be lateralized in this species. Twelve male Bengalese finches were trained by operant conditioning to discriminate between a Bengalese finch song and a zebra finch song. Before training, the left HVc was lesioned in four birds and the right HVc was lesioned in four other birds. The remaining four birds were used as controls without surgery. Birds with a left HVc lesion required significantly more time to learn to discriminate between the two songs than did birds with a right HVc lesion or intact control birds. These results suggest that the left HVc is not only dominant for the motor control of song, but also for the perceptual discrimination of song. Accepted after revision: 11 September 2001 Electronic Publication     

I know you are not looking at me: capuchin monkeys’ (<Emphasis Type="Italic">Cebus apella</Emphasis>) sensitivity to human attentional states

The present study asked whether capuchin monkeys recognize human attentional states. The monkeys requested food from the experimenter by extending an arm (pointing) toward the baited one of two transparent cups. On regular trials the experimenter gave the food immediately to the monkeys upon pointing but on randomly inserted test trials she ignored the pointing for 5 s during which she displayed different attentional states. The monkeys looked at the experimenter's face longer when she looked at the monkeys than when she looked at the ceiling in Experiment 1, and longer when she oriented her head midway between the two cups with eyes open than when she did so with eyes closed in Experiment 2. However, the monkeys showed no differential pointing in these conditions. These results suggest that capuchins are sensitive to eye direction but this sensitivity does not lead to differential pointing trained in laboratory experiments. Furthermore, to our knowledge, this is the first firm behavioral evidence that non-human primates attend to the subtle states of eyes in a food requesting task.     

Projecting two words with one machine: Presenting two different visual stimuli using just one projector without viewers’ noticing the duality

A new method, named the fMORI technique, for presenting two different visual stimuli using just one video projector without the viewers' noticing the duality is introduced along with several sample applications of this presentation method. The LCD projectors available now have three color LCD panels aligned differently in terms of their polarization, polarizing differently the green and magenta (red plus blue) components of its emitting image. Therefore, two visual stimuli either in green or in magenta projected on thesame screen canbe observed separately by subjects wearing an appropriate polarizing filter. This is a variation of the MORI technique (Mori, 2003, 2007b) but it requires only one video projector rather than two. Full-color movies cannot be presented with the fMORI technique, but it may be utilized in various research areas in which only static monochrome visual stimuli, such as words or numbers, are used.