One, two, three, four, or is there something more? Numerical discrimination in day-old domestic chicks

Human adults master sophisticated, abstract numerical calculations that are mostly based on symbolic language and thus inimitably human. Humans may nonetheless share a subset of non-verbal numerical skills, available soon after birth and considered the evolutionary foundation of more complex numerical reasoning, with other animals. These skills are thought to be based on the two systems: the object file system which processes small values (<3) and the analogue magnitude system which processes large magnitudes (>4). Infants’ ability to discriminate 1 vs. 2, 1 vs. 3, 2 vs. 3, but not 1 vs. 4, seems to indicate that the two systems are independent, implying that the conception of a continuous number processing system is based on precursors that appear to be interrupted at or about the number four. The findings from the study being presented here indicating that chicks are able to make a series of discriminations regarding that borderline number (1 vs. 4, 1 vs. 5, 2 vs. 4) support the hypothesis that there is continuity in the number system which processes both small and large numerousness.     

Minds of their own

by Lesley J. Rogers, Allen & Unwin, 1997. $16.95 (x+212 pages) ISBN 1 86448 504 3.     

The Individuation Process in Post-Modernity

C. G. Jung defined individuation as the process of differentiation from the general collective psychology—from the norms and the values of the society in which the individual is immersed. Accordingly, individuation occurs in relation to the culture of the time and the zeitgeist. During the second half of life, the process, according to Jung, takes the shape of a lifetime dynamic dialogue between the ego and the unconscious contents, aiming to reach psychic completeness. One of the participants in this dialogue is the ego, and since the ego necessarily develops inside a culture, this part of the individuation process also occurs in relation to the culture of the time. We are now fully immersed in post-modernity, and the zeitgeist is represented by the society of technology. In relation to this totally new scenario, do we still deal with the same individuation process described by Jung? How many of our patients confront themselves with the Self and its symbols, stepping toward some kind of psychic totality? This article hints at different forms of individuation reflective of our post-modern technologically dominated times, and it touches upon the concept of the end of meaning and the “death of God.” Considering this epochal passage, we might be compelled to outline a further form of individuation: that of a conscious revolt of the ego toward its basic ingredients (will to power, primary narcissism, and need of identity) and toward the old image of the Self, so similar to that God that should be dead.     

Chicks prefer to peck at insect-like elongated stimuli moving in a direction orthogonal to their longer axis

Spontaneous preferences towards possible prey have been little investigated using targets in motion. Preferences of domestic chicks (Gallus gallus) to peck at video-images of stimuli representing live insects moving along their longer body axis (i.e. “forwards”) or along the shorter body axis (i.e. “sideways”) were investigated. Chicks presented with both types of stimulus displayed a significant preference for pecking at stimuli moving sideways. This preference was already present on day 1 post-hatching, and it strengthened on day 6 for those chicks that had experienced pecking at live insects. Head angles used to fixate the stimuli prior to pecking were also analysed and were consistent (i.e. 30°–35° and 60°–65°) with those reported for fixation of non-edible targets (larger stimuli at a distance). In a first control experiment the same video-presented stimuli were used but the insect’s legs were removed to reduce flickering. In a second control experiment, paper-printed images of the whole insect were used. In both cases, the sideways direction of movement was clearly preferred. Overall, our data show that chicks have a spontaneous preference to peck at video-images resembling live insects moving along their shorter body axis. Sideways movement may constitute a crucial signal attracting chicks’ attention and enhancing predatory responses possibly because of stronger stimulation of motion detectors.     

Mom’s shadow: structure-from-motion in newly hatched chicks as revealed by an imprinting procedure

The ability to recognize three-dimensional objects from two-dimensional (2-D) displays was investigated in domestic chicks, focusing on the role of the object’s motion. In Experiment 1 newly hatched chicks, imprinted on a three-dimensional (3-D) object, were allowed to choose between the shadows of the familiar object and of an object never seen before. In Experiments 2 and 3 random-dot displays were used to produce the perception of a solid shape only when set in motion. Overall, the results showed that domestic chicks were able to recognize familiar shapes from 2-D motion stimuli. It is likely that similar general mechanisms underlying the perception of structure-from-motion and the extraction of 3-D information are shared by humans and animals. The present data shows that they occur similarly in birds as known for mammals, two separate vertebrate classes; this possibly indicates a common phylogenetic origin of these processes.     

Multiple 3-D interpretations in a classic stereokinetic effect

It is known that a flat ellipse rotating in the frontoparallel plane sooner or later appears as a rigid circular disc tilting in 3-D space. An experiment is reported in which prolonged exposure to the same flat pattern produces a second previously unnoticed 3-D percept: an elongated egg slanted in 3-D space, which points towards the observer and the end parts of which describe a circular trajectory in the frontal plane. It is shown that the achievement of this alternative percept is not affected by the particular shape of the ellipse, although the time needed to reach it increases with an ellipse with a 2:3 axis ratio.     

Subjective contours can produce stereokinetic effects

When a pattern of interrupted concentric circles drawn so as to produce an anomalous contour ellipse is slowly rotated in the frontoparallel plane, the subjective figure appears first to deform and then to tilt as a ring in 3-D space over motionless circles. Also, Benussi's floating cone can be obtained by placing an eccentric gray dot upon an anomalous solid ellipse and setting this figure into rotation. These patterns provide strong evidence that subjective contours can produce stereokinetic effects as effectively as real contours can. Implications for current explanations of stereokinetic effects are presented and discussed.     

Sex differences in social reinstatement motivation of the domestic chick (Gallus gallus) revealed by runway tests with social and nonsocial reinforcement

Male and female chicks (Gallus gallus) were trained at 4 days old to run along a corridor to reach a goal box that contained either cagemates (social reinforcement) or food (nonsocial reinforcement). Females ran faster when social reinforcement was used, whereas males ran faster with nonsocial reinforcement. When social reinforcement was used with a V-shaped runway, in which chicks had to proceed toward the goal object in an indirect fashion, sex differences were reversed. The results may be due to stronger social reinstatement tendencies in females than in males: Higher levels of social motivation facilitate behavioral performance when the task is easy (straight runway) and inhibit it when the task is difficult (V-shaped runway).