Simultaneous Discrimination Learning in Chicks: Spatial Representations and Object Characteristics

Chicks were trained to discriminate (1) between two boxes of the same colour on the basis of their positions; (2) between two boxes of different colours on the basis of their positions or on the basis of their colours. No significant differences between these tasks appeared. Addition of colour and position improved learning when the boxes were entirely coloured but not when differently coloured discs were placed over the lids of two identical boxes. It is argued that in simultaneous discrimination learning chicks rely primarily on the “relative” position of the goal objects (i. e. in relation to each other) and utilize featural information (colour) to segregate the goal objects as distinct perceptual units. Results also stressed the role of “object characteristics” as opposed to the traditional notion of “cues”.     

Defining Natural Categories in Acoustic Signals: Comparison of Three Methods Applied to ‘Chick-a-dee’ Call Notes

Chicks were trained to discriminate between two identical boxes on the basis of their position. Subsequently, the colour of parts of the positive (reinforced) box was changed and chicks were retrained. Results showed that chicks were more or less impaired during retraining depending on the spatial distribution of the changed stimuli. Chicks behaved as if a figure (a disc or a spot of dots) painted on a box was irrelevant to them, whereas they did respond to changes in the colour of a uniformly coloured box or of scattered dots painted on a box. Similar results were obtained in simultaneous discrimination learning tasks involving addition of cues (e.g. colour plus position). Addition of cues facilitated learning using boxes the same colour all over or with painted scattered dots, but not using boxes with a disc or a spot of dots. Furthermore, addition of shape and position information had different outcomes depending on the use of three-dimensional objects or of painted figures: learning facilitation occurred only using three-dimensional objects. Results are interpreted in terms of an “object hypothesis”, and the validity and usefulness of traditional terms such as cues is questioned.     

Learning of colour and position cues in domestic chicks: Males are better at position,females at colour

Male and female chicks were trained to discriminate between two boxes for food reinforcement. The correct box was indicated by a colour cue (red or brown) and a position cue (right or left). After learning, the colour and the position cues were dissociated: the right-left location of the two boxes was alternated between trials according to a semi-random sequence.The chicks were thus retrained to discriminate either on the basis of colour (irrespective of position) or on the basis of position (irrespective of colour). There were no sex differences, during training, with both position and colour cues. However, during re-training females performed better on the colour learning task and males performed better on the position learning task.     

Order error in the calculation of continuous relative phase

The aims of this study were to demonstrate “order error” in the calculation of continuous relative phase (CRP) and to suggest two alternative methods—(i) constructing phase-plane portraits by plotting position over velocity; and (ii), the Hilbert transform—to rectify it. Order error is the change of CRP order between two degrees of freedom (e.g., body segments) when using the conventional method of constructing phase-plane portraits (i.e., velocity over position). Both sinusoidal and non-sinusoidal simulated signals as well as signals from human movement kinematics were used to investigate order error and the performance of the two alternative methods. Both methods have been shown to lead to correct results for simulated sinusoidal and non-sinusoidal signals. For human movement data, however, the Hilbert transform is superior for calculating CRP.     

The Problem Realm and the World of Inner Experiences of Upper-Grade Students

In her chapter, the author understands ‘problems’ not as problems of solving learning tasks, but life situations which a young person has to solve. Such situations are often negative experiences. The author claims that problem situations can only be evaluated on the basis of ‘perezhivanie’ associated with them. This aspect is seldom present in psychological-pedagogical research. Most research starting from the 1920’s uses personal diaries or observations as the methods of studying life problems. But they are not able to reveal objectively relations between life problems and their ‘perezhivanie.’ The author introduces two new survey methods called “the world of perezhivanie” and “panorama of problems,” with which primary material is collected for further elaboration of the relation between problem domains and ‘perezhivanie.’ The chapter presents new methods of collecting data. Empirical results are published in other journals and books.     

A new conception of the shoot of higher plants

According to the classical model, the “shoot” consists only of the categories “caulome” (“stem” sensu lato) and “phyllome” (“leaf” sensu lato), (and “root” in cases of “adventitious” root formation). If lateral shoots are present, their position is axillary. Consequently, caulome as well as phyllome are inserted on the caulome and only on the caulome. This classical model of the shoot has two disadvantages of great consequence: (1) Intermediate organs cannot be accepted as such, but have to be interpreted (i.e. categorized) as either caulome or phyllome (or root) by distortion of the actual similarity. (2) Certain positional changes of organs cannot be accepted as such, but have to be “explained” by congenital fusion. The new conception of the shoot will have the advantages of the classical model but not its disadvantages. Hence, the shoot may consist of the following parts: (main and lateral) shoot, caulome, phyllome, root, emergence, and structures intermediate between (i.e. partially homologous to) any of the preceding. Thus, the five categories of the classical model, namely “shoot”, “caulome”, “phyllome”, “root” and “emergence” are no longer mutually exclusive; they may merge into each other due to an actual or potential continuum. Intermediate organs are therefore accepted as such; for example, an organ may be characterized as an intermediate form between a caulome and a phyllome. Besides intermediate forms, all changes in position are accepted as such. Hence, the following positional relations are possible: caulome and phyllome may be inserted on the caulome, caulome and phyllome may be inserted on the phyllome; roots may be inserted on caulome or phyllome; intermediate forms may be inserted on the caulome, phyllome, or other intermediate forms. Consequences of the new conception for morphological research are pointed out, especially for homologization, evolutionary considerations, and the direction in which research progresses.     

Nonlinear cross-frequency interactions in primary auditory cortex spectrotemporal receptive fields: a Wiener–Volterra analysis

The effects of nonlinear interactions between different sound frequencies on the responses of neurons in primary auditory cortex (AI) have only been investigated using two-tone paradigms. Here we stimulated with relatively dense, Poisson-distributed trains of tone pips (with frequency ranges spanning five octaves, 16 frequencies /octave, and mean rates of 20 or 120 pips /s), and examined within-frequency (or auto-frequency) and cross-frequency interactions in three types of AI unit responses by computing second-order “Poisson-Wiener” auto- and cross-kernels. Units were classified on the basis of their spectrotemporal receptive fields (STRFs) as “double-peaked”, “single-peaked” or “peak-valley”. Second-order interactions were investigated between the two bands of excitatory frequencies on double-peaked STRFs, between an excitatory band and various non-excitatory bands on single-peaked STRFs, and between an excitatory band and an inhibitory sideband on peak-valley STRFs. We found that auto-frequency interactions (i.e., those within a single excitatory band) were always characterized by a strong depression of (first-order) excitation that decayed with the interstimulus lag up to ～200 ms. That depression was weaker in cross-frequency compared to auto-frequency interactions for ～25% of dual-peaked STRFs, evidence of “combination sensitivity” for the two bands. Non-excitatory and inhibitory frequencies (on single-peaked and peak-valley STRFs, respectively) typically weakly depressed the excitatory response at short interstimulus lags (<50 ms), but weakly facilitated it at longer lags (～50–200 ms). Both the depression and especially the facilitation were stronger for interactions with inhibitory frequencies rather than just non-excitatory ones. Finally, facilitation in single-peaked and peak-valley units decreased with increasing stimulus density. Our results indicate that the strong combination sensitivity and cross-frequency facilitation suggested by previous two-tone-paradigm studies are much less pronounced when using more temporally-dense stimuli.     

Cytotaxonomical Studies of Tea Plants

Nine forms of Camellia sinensis (L) Kuntze from Guizhou, Yunnan, Sichuan and Fujian Provinces were cytotaxonomically studied in this work. The wall degradation hypotonic method was used for preparing chromosome samples which were stained in Giemsa. The micrographs of their somatic metaphase are shown in Plates 1-2, the ranges of chromosome relative lengths, arm ratios, karyotype formulae and classification of karyotypes according to Li and Chen (1985) are shown in Table 1 and the idiograms in Fig. l. The main points are mentioned as follows: (1) All these forms are found to be diploid with 2n = 30, and they are reported for the first time except Yunnan(Fengqing)cultivated form. (2) All the karyotypes of the forms examined are relatively uniform, which reveal the gradual decrease in size from the longest to the shortest chromosomes, similar chromosomal relative length, smaller chromosome types varying between 2- 5μm. The karyotype mainly consists of metacentric (m) and submetacentric (sm) chromosomes. Sat-chromosomes are difficult to be discovered on mid -metaphase chromosomes. The cytological information confirms the close relationship among these tea forms. (3) According to the asymmetry of karyotype, the nine tea forms are divided into two types: one consists of the arbor with macrophyll, i.e. Guizhou and Yunnan( Fengqing and Tengchong)cultivated forms, which have the”2A” karyotype possessing metacentric(m) and submetacentric(sm) chromosomes. The karyotypes might be of the most symmetrical or primitive type ;the other consists of the bush or microarbor with mostly medium- and microphyll, less frequently macrophyll, i.e. Qianmei 419, Qianmei 502, Yaan,Fuding, Sichuan and Qianmei 101 cultivated forms, which have the “2A” and “2B” karyotypes, consisting of metacentric (m), submetacentric (sm) and a pair of subtelocentric (st) chromosomes, and more asymmetrical than that of the first karyotype. They might be more advanced. (4) In recent years, two subspecies, i.e. ssp. “yunnan”and ssp. “bohea”, including seven varieties, in C. sinensis were recognized but not formally published by Zhuang et al. (1981). From the present work and the previous reports the authors agree with Zhuang’s classification, because recognition of two subspecies is remarkably consistent with the two kinds of karyotypes reported here. C.sinensis ssp. “yunnan” with arbor and macrophyll characters has more symmetrical karyotype than that of C. sinensis ssp. “bohea” with bush or microarbor and mostly mediumand microphyll characters. That is to say, ssp.”yunnan” is more primitive than ssp. “bohea”. (5) Based on the karyotype analysis of arbor and macrophyll teas reported before and here (see Table 3), the authors support the viewpoint that YunnanGui zhou Plateau is the original center of tea Plants, whereas Assam form in In-dia is derived.     

Genetic-gonadal-genitals sex (3G-sex) and the misconception of brain and gender,or, why 3G-males and 3G-females have intersex brain and intersex gender

The categorization of individuals as “male” or “female” is based on chromosome complement and gonadal and genital phenotype. This combined genetic-gonadal-genitals sex, here referred to as 3G-sex, is internally consistent in ~99% of humans (i.e., one has either the “female” form at all levels, or the “male” form at all levels). About 1% of the human population is identified as “intersex” because of either having an intermediate form at one or more levels, or having the “male” form at some levels and the “female” form at other levels. These two types of “intersex” reflect the facts, respectively, that the different levels of 3G-sex are not completely dimorphic nor perfectly consistent. Using 3G-sex as a model to understand sex differences in other domains (e.g., brain, behavior) leads to the erroneous assumption that sex differences in these other domains are also highly dimorphic and highly consistent. But parallel lines of research have led to the conclusion that sex differences in the brain and in behavior, cognition, personality, and other gender characteristics are for the most part not dimorphic and not internally consistent (i.e., having one brain/gender characteristic with the “male” form is not a reliable predictor for the form of other brain/gender characteristics). Therefore although only ~1% percent of humans are 3G-“intersex”, when it comes to brain and gender, we all have an intersex gender (i.e., an array of masculine and feminine traits) and an intersex brain (a mosaic of “male” and “female” brain characteristics).     

In and out: Effects of shoot- vs. rooted-presence sampling methods on plant diversity measures in mountain grasslands

Plant diversity measures (e.g., alpha- and beta-diversity) provide the basis for a number of ecological indication and monitoring methods. These measures are based on species counts in sampling units (plots or quadrats). However, there are two alternative conventions for defining a vascular plant species as “present” in a plot, i.e. “shoot presence” (a species is recorded if the vertical projection of any above-ground part falls within the plot) and “rooted presence” (a species is recorded only when an individual is rooted inside the plot). Very few studies addressed the effects of the two sampling conventions on species richness and diversity indices. We sampled mountain dry grasslands in Italy across different plot sizes and vegetation types to assess how large is the difference in alpha- and beta-diversity values and in sample-based rarefaction curves between the two methods. We found that the difference is greatly dependent on plot size, being more relevant, both in absolute and percentage values, at smaller grain; it is also dependent on habitat type, being larger in shallow-soil communities, as they have a sparser vegetation structure and host life-form types with a larger lateral spread. At fine spatial scales (<1 m²) the difference is large enough to bias statistical inference, and we conclude that at such scales one should not attempt to compare plant diversity indices if they were not obtained with the same sampling convention.     

Honeybee navigation: linear perception of short distances travelled

Recent evidence indicates that honeybees measure distance flown to a food source by integrating, over time, the apparent visual motion of the environment that they experience en route to the goal. Is the bee's perception of distance travelled a linear function of distance, or is it some other function? This question was investigated by training bees to fly into a tunnel and receive a food reward. The walls and floor of the tunnel were lined with a random texture, and the reward was placed at one of two fixed distances, “near” or “far”, from the tunnel entrance. The feeder containing the reward was placed in a box which could be accessed through one of two openings, one on the left side of the box, and the other on the right. When the box was at the “near” position, the reward could only be accessed through the left-hand opening; when the box was at the “far” position, the reward could only be accessed through the right-hand opening. When the trained bees were tested individually in an identical, fresh tunnel with the reward removed from the box, they showed a strong preference for the left-hand opening when tested at the “near” distance, and for the right-hand opening when tested at the “far” distance. At intermediate positions, the bees' preference for the two openings varies linearly with distance. These findings suggest that the honeybee's perception of distance travelled is linear, at least over the distances and range of image motions experienced in our experiments. The implications for navigation and for the encoding of distance information in the dance are discussed.     

A molecular dynamics investigation of chiral discrimination complexes as chiral stationary-phase models: Methyl N-(2-naphthyl)alaninate with N-(3,5-dinitrobenzoyl)leucine n-propylamide

Molecular dynamics simulations were performed on complexes of (S)-methyl N-(2-naphthyl)alaninate (NAP) with the enantiomers of N-(3,5-dinitrobenzoyl)leucine n-propylamide (DNB), which are used as models for chiral stationary-phase systems developed by Pirkle and co-workers. These studies were undertaken to qualitatively examine (pictorially) the role of entropic effects in these systems. The results of the dynamics calculations were used to refine the search for low-energy conformers. The structures were refined by the use of BioDesign's molecular mechanics method implemented in Biograf. The results of the structural refinements support our previous observation that the SR complex can achieve the same three primary interactions which are observed in the SS structure (i.e., two intermolecular hydrogen bonds and pi stacking) without a significant increase in energy. In addition, these primary interactions are conserved during molecular dynamics simulations with the occurrence of conformations which differ only in the rotational states of the alkyl side chains and ester group (which bears two potential hydrogen bond acceptors utilized in both the homo- and heterochiral complexes). The major difference in the two complexes is the relative position of the sec-butyl group and hydrogen atom on DNB's chiral center, both of which are outside the primary interaction region. All other local minima which have different relative pi orientations (“front–back,” “back–back,” and “back–front” as defined herein) are not sufficiently populated to make more than a negligible contribution to the statistical (time- or energy-averaged) analysis of the (SS)- and (SR)-NAP–DNB complexes. Thus the entropic effects observed in this study (e.g., alkyl side chain or ester group rotations) do not show evidence of qualitative differential effects on the maintenance of the same three primary interactions by both the homo- and heterochiral complexes. The reliability of the present study, which provides pictorial representations of the entropic effects, is not sufficient to determine whether the entropic effects observed herein are sufficient to achieve enantiomeric discrimination alone or in conjunction with other factors (e.g., conformational strain energy). Thus, all of the computational studies we have performed to date (i.e., our previous studies, which include strain energy and through-space field effects, and the present study, which includes entropic effects) show no evidence of any qualitative difference in the homo- and heterochiral complexes in terms of maintaining the same three “contact points”.     

Adoption by captive parturient rhesus macaques: Biological vs. adopted infants and the cost of being a “twin” and rearing “twins”

Four rhesus macaque (Macaca mulatta) mothers each spontaneously adopted and reared an abandoned, unrelated neonate in addition to their own neonate. Data on relative time spent in maternal contact and who maintained proximity were collected for the biological and adopted “twins” and singleton control infants using focal animal sampling. Infant weight gain and the subsequent conception history for each mother were obtained for the following year. Biological infants spent more time in maternal contact than their adopted “twin” siblings. When in contact with their mothers, biological “twins” spent more time in the ventro-ventral position and more ventral time alone than adoptees. Mothers initiated more contacts with their biological infants than their adopted infants, suggesting these differences may be due to differential maternal behavior. “Twins” gained weight at a slower rate than singletons, and mothers rearing “twins” produced significantly fewer offspring the following season. Am. J. Primatol. 43:259–264, 1997. © 1997 Wiley-Liss, Inc.     

Interactive effects between diet and genotypes of host and pathogen define the severity of infection

Host resistance and parasite virulence are influenced by multiple interacting factors in complex natural communities. Yet, these interactive effects are seldom studied concurrently, resulting in poor understanding of host‐pathogen‐environment dynamics. Here, we investigated how the level of opportunist pathogen virulence, strength of host immunity and the host condition manipulated via diet affect the survival of wood tiger moth Parasemia plantaginis (Arctidae). Larvae from “low cuticular melanin” and “high cuticular melanin” (considered as low and high pathogen resistance, respectively) selection lines were infected with moderately and highly virulent bacteria strains of Serratia marcescens, while simultaneously manipulating host diet (with or without antibacterial compounds). We measured host survival and food preference before and after infection to test whether the larvae “self‐medicate” by choosing an anti‐infection diet (Plantago major, i.e., plantain leaf) over lettuce (Lactuca sativa). “High melanin” larvae were more resistant than “low melanin” larvae to the less virulent strain that had slower growth and colonization rate compared with the more virulent strain. Cuticular melanin did not enhance survival when the larvae were infected with the highly virulent strain. Anti‐infection diet enhanced survival of the “high melanin” but not the “low melanin” hosts. Survival was dependent on family origin even within the melanin selection lines. Despite the intrinsic preference for lettuce, no evidence of self‐medication was found. These results demonstrate that the relative benefit of host cuticular melanin depends on both diet and pathogen virulence: plantain diet only boosted the immunity of already resistant “high melanin” hosts, and cuticular melanin increased host survival only when infected with moderately virulent pathogen. Moreover, there was considerable variation in host survival between families within both melanin lines suggesting genetic basis for resistance. These results indicate that although melanin is an important predictor of insect immunity, its effect on disease outcomes greatly depends on other interacting factors.     

The individual nest box as a super-stimulus for domestic hens

Following reports of inconsistent nest choice by hens in groups, choice of nest boxes by solitary hens was investigated. Thirty-two hens of a White Leghorn strain were each isolated with six nest boxes while they laid six eggs. From 16 hens, eggs were collected daily. Only one of these birds laid all her eggs in one nest box, and others used up to four boxes. The other 16 were allowed to accumulate eggs, and these were significantly more consistent in nest choice. Five used only one box. However, the other 11 of this group showed incomplete consistency.An explanation for inconsistent nest choice was suggested by a second experiment. The importance of enclosure in nest-site selection was tested in hens of White Leghorn and Rhode Island Red strains. Individuals about to lay their first egg were isolated with a choice of two types of nest box, selected from five types of different enclosure. Exposed nests, of similar dimensions to natural nests, were rarely used by either strain. By contrast, more enclosed nests were strongly selected. These results indicate that enclosure is an important stimulus in nest-site selection, and that artificial nest boxes, which are more enclosed than natural sites, act as super-normal stimuli (or “super-stimuli”). Choices between super-stimuli are likely to be equivocal, which accounts for inconsistency in the use of nest boxes and other features of the nesting behaviour of domestic hens.     

"Noise" as a unifying concept in the theory of schizophrenia

The psychological effects of pharmacologically active substances can only be adequately described in terms of the psychological processes upon which they act. Psychopharmacology therefore depends on the development of psychological “models”, i.e. formally stated and testable hypotheses concerning the psychological processes required for the performance of any given task. Information theory is not concerned with the physical nature of events but only with those features which confer specificity upon them. It therefore provides a suitable theoretical language in which to describe interactions between biochemical, neurophysiological and psychological events. (i) The first section of this paper defines the information-theory concept of noise. Starting from first principles with the “noisy channel” and progressing to the “noisy system”, some of its psychophysiological implications are explored. (ii) An “order-memory” task is described which was used for three years to study the thinking of acutely disturbed young adult psychiatric patients, including many with acute schizophrenia. On the basis of a simple model, it is possible to calculate the value of a “critical” noise-level which marks the dividing line between two qualitatively different modes of functioning. (iii) A number of results are either reported or summarized, which show the functional significance of a supra-critical noise-level and its connection with the acute schizophrenic state. (iv) A “control-theory” approach to schizophrenia is outlined, which shows how specific and non-specific hereditary factors could be accommodated in the hypothesis but mainly emphasizes the concept of a mutual struggle for control between parent and child, in which the “loser” overloads the regulatory capacity of the other by “going noisy”. In this way the “loser” escapes from control but is more or less disabled by his own cognitive noise.     

Awareness during electromyographic biofeedback: Of signal or process?

During relaxation training, awareness of trial-to-trial changes in frontalis-muscle tension levels was assessed with and without auditory electromyographic(EMG) biofeedback. Immediately after each 128-sec training trial, the subject was required to guess whether muscle tension indexed by EMG activity increased(“Up”) or decreased(“Down”) relative to the immediately preceding trial. The probability of correct guessing, P(c), improved as the absolute difference in EMG increased between trials only when biofeedback was presented. For subjects not receiving biofeedback, P(c) remained low even when the absolute difference between trials was large. Subjects in each condition employed a strategy to guess “Down” more often consistent with the expectation that they were being trained to relax. The “Down” set strategy was shown to be separable from the informational basis of P(c) provided by biofeedback. This procedure can be employed to evaluate central assumptions of biofeedback relating to posttraining awareness of changes in muscle tension and the relationship between awareness and control of muscle tension.     

The Alacoil: A very tight,antiparallel coiled-coil of helices

The Alacoil is an antiparallel (rather than the usual parallel) coiled-coil of α-helices with Ala or another small residue in every seventh position, allowing a very close spacing of the helices (7.5–8.5 Å between local helix axes), often over four or five helical turns. It occurs in two distinct types that differ by which position of the heptad repeat is occupied by Ala and by whether the closest points on the backbone of the two helices are aligned or are offset by half a turn. The aligned, or ROP, type has Ala in position “d” of the heptad repeat, which occupies the “tip-to-tip” side of the helix contact where the Cα–Cβ bonds point toward each other. The more common offset, or ferritin, type of Alacoil has Ala in position “a” of the heptad repeat (where the Cα-Cβ bonds lie back-to-back, on the “knuckle-touch” side of the helix contact), and the backbones of the two helices are offset vertically by half a turn. In both forms, successive layers of contact have the Ala first on one and then on the other helix. The Alacoil structure has much in common with the coiled-coils of fibrous proteins or leucine zippers: both are α-helical coiled-coils, with a critical amino acid repeated every seven residues (the Leu or the Ala) and a secondary contact position in between. However, Leu zippers are between aligned, parallel helices (often identical, in dimers), whereas Alacoils are between antiparallel helices, usually offset, and much closer together. The Alacoil, then, could be considered as an “Ala anti-zipper.” Leu zippers have a classic “knobs-into-holes” packing of the Leu side chain into a diamond of four residues on the opposite helix; for Alacoils, the helices are so close together that the Ala methyl group must choose one side of the diamond and pack inside a triangle of residues on the other helix. We have used the ferritin-type Alacoil as the basis for the de novo design of a 66-residue, coiled helix hairpin called “Alacoilin.” Its sequence is: cmSP DQWDKE A AQYDAHA QE FEKKS HRNng TPEA DQYRHM A SQY QAMA QK LKAIA NQLKK Gseter (with “a” heptad positions underlined and nonhelical parts in lowercase), which we will produce and test for both stability and uniqueness of structure.     

Introduced Drosophila subobscura populations perform better than native populations during an oviposition choice task due to increased fecundity but similar learning ability

The success of invasive species is tightly linked to their fitness in a putatively novel environment. While quantitative components of fitness have been studied extensively in the context of invasive species, fewer studies have looked at qualitative components of fitness, such as behavioral plasticity, and their interaction with quantitative components, despite intuitive benefits over the course of an invasion. In particular, learning is a form of behavioral plasticity that makes it possible to finely tune behavior according to environmental conditions. Learning can be crucial for survival and reproduction of introduced organisms in novel areas, for example, for detecting new predators, or finding mates or oviposition sites. Here we explored how oviposition performance evolved in relation to both fecundity and learning during an invasion, using native and introduced Drosophila subobscura populations performing an ecologically relevant task. Our results indicated that, under comparable conditions, invasive populations performed better during our oviposition task than did native populations. This was because invasive populations had higher fecundity, together with similar cognitive performance when compared to native populations, and that there was no interaction between learning and fecundity. Unexpectedly, our study did not reveal an allocation trade‐off (i.e., a negative relationship) between learning and fecundity. On the contrary, the pattern we observed was more consistent with an acquisition trade‐off, meaning that fecundity could be limited by availability of resources, unlike cognitive ability. This pattern might be the consequence of escaping natural enemies and/or competitors during the introduction. The apparent lack of evolution of learning may indicate that the introduced population did not face novel cognitive challenges in the new environment (i.e., cognitive “pre‐adaptation”). Alternatively, the evolution of learning may have been transient and therefore not detected.     

Spatial compatibility and position of the effectors

Mean reaction times obtained with crossed hands (right had on the left and left hand on the right) are slower than reaction times obtained with uncrossed hands (right hand on the right and left hand on the left). These results have been explained as a compatibility effect between the responding hand and its spatial position. The goal of the present experiment was to establish whether the position of the hand is encoded by the subjects relative to their body (absolute position) or relative to the other hand (relative position). The subjects performed a discrimination task on two visual stimuli. Stimuli and hands were either on the same side of the body (both on the left or both on the right) or had different absolute position. In all conditions the subjects responded with crossed and uncrossed hands. The results support the hypothesis that relative position is encoded.