Implication of the visual system in the regulation of activity cycles in the absence of solar light: 2-[I-125]iodomelatonin binding sites and melatonin receptor gene expression in the brains of demersal deep-sea gadiform fish

Relative eye size, gross brain morphology and central localization of 2-[I-125]iodomelatonin binding sites and melatonin receptor gene expression were compared in six gadiform fish living at different depths in the north-east Atlantic Ocean: Phycis blennoides (capture depth range 265-1260 m), Nezumia aequalis (445-1512 m), Coryphaenoides rupestris (706-1932 m), Trachyrincus murrayi (1010-1884 m), Coryphaenoides guentheri (1030 m) and Coryphaenoides (Nematonurus) armatus (2172-4787 m). Amongst these, the eye size range was 0.15-0.35 of head length with a value of 0.19 for C.(N.) armatus, the deepest species. Brain morphology reflected behavioural differences with well-developed olfactory regions in P.blennoides, T.murrayi and C. (N.) armatus and evidence of olfactory deficit in N. aequalis, C. rupestris and C. guentheri. All species had a clearly defined optic tectum with 2-[I-125] iodomelatonin binding and melatonin receptor gene expression localized to specific brain regions in a similar pattern to that found in shallow-water fish. Melatonin receptors were found throughout the visual structures of the brains of all species. Despite living beyond the depth of penetration of solar light these fish have retained central features associated with the coupling of cycles of growth, behaviour and reproduction to the diel light-dark cycle. How this functions in the deep sea remains enigmatic.

Visual function: How spiders find the right rock to crawl under

Animals that go on hunting expeditions face the problem of finding the way home at the end of the day. A group of hunting spiders has now been added to the list of animals that use the celestial pattern of polarized light as a compass for navigation. (C) 1999 Elsevier Science Ltd. All rights reserved.

Social identity and self-categorization processes in organizational contexts

Although aspects of social identity theory are familiar to organizational psychologists, its elaboration, through self-categorization theory, of how social categorization and prototype-based depersonalization actually produce social identity effects is less well known. We describe these processes, relate self-categorization theory to social identity theory, describe new theoretical developments in detail, and show how these developments can address a: range of organizational phenomena. We discuss cohesion and deviance, leadership, subgroup and sociodemographic structure, and mergers and acquisitions.

Effect of density on spatial distribution, pit formation and pit diameter of Myrmeleon acer Walker, (Neuroptera : Myrmeleontidae): patterns and processes

The effect of increasing population density on the formation of pits, their size and spatial distribution, and on levels of mortality was examined in the antlion Myrmeleon acer Walker. Antlions were kept at densities ranging from 0.4 to 12.8 individuals per 100 cm(2). The distribution of pits was regular or uniform across all densities, but antlions constructed proportionally fewer and smaller pits as density increased. Mortality through cannibalism was very low and only occurred at densities greater than five individuals per 100 cm(2). Antlions in artificially crowded situations frequently relocated their pits and when more space became available, individuals became more dispersed with time. Redistribution of this species results from active avoidance of other antlions and sand throwing associated with pit construction and maintenance, rather than any attempt to optimise prey capture per se.

Spectral tuning and the visual ecology of mantis shrimps

The compound eyes of mantis shrimps (stomatopod crustaceans) include an unparalleled diversity of visual pigments and spectral receptor classes in retinas of each species. We compared the visual pigment and spectral receptor classes of 12 species of gonodactyloid stomatopods from a variety of photo environments, from intertidal to deep water ( > 50 m), to learn how spectral tuning in the different photoreceptor types is modified within different photic environments. Results show that receptors of the peripheral photoreceptors, those outside the midband which are responsible for standard visual tasks such as spatial vision and motion detection, reveal the well-known pattern of decreasing lambda(max) with increasing depth. Receptors of midband rows 5 and 6, which are specialized for polarization vision, are similar in all species, having visual lambda(max)-values near 500 nm, independent of depth. Finally the spectral receptors of midband rows 1 to 4 are tuned for maximum coverage of the spectrum of irradiance available in the habitat of each species. The quality of the visual worlds experienced by each species we studied must vary considerably, but all appear to exploit the full capabilities offered by their complex visual systems.

The effects of change in lead stimulus modality on the modulation of acoustic blink startle

In two experiments we investigated the effect of generalized orienting induced by changing the modality of the lead stimulus on the modulation of blink reflexes elicited by acoustic stimuli. In Experiment 1 (n = 32), participants were presented with acoustic or visual change stimuli after habituation training with tactile lead stimuli. In Experiment 2 (n = 64), modality of the lead stimulus (acoustic vs. visual) was crossed with experimental condition (change vs. no change). Lead stimulus change resulted in increased electrodermal orienting in both experiments. Blink latency shortening and blink magnitude facilitation increased from habituation to change trials regardless of whether the change stimulus was presented in the same or in a different modality as the reflex-eliciting stimulus. These results are not consistent with modality-specific accounts of attentional startle modulation.

Quantum measurement and stochastic processes in mesoscopic conductors

In quantum measurement theory it is necessary to show how a, quantum source conditions a classical stochastic record of measured results. We discuss mesoscopic conductance using quantum stochastic calculus to elucidate the quantum nature of the measurement taking place in these systems. To illustrate the method we derive the current fluctuations in a two terminal mesoscopic circuit with two tunnel barriers containing a single quasi bound state on the well. The method enables us to focus on either the incoming/ outgoing Fermi fields in the leads, or on the irreversible dynamics of the well state itself. We show an equivalence between the approach of Buttiker and the Fermi quantum stochastic calculus for mesoscopic systems.

Dual processes in recognition: Does a focus on measurement operations provide a sufficient foundation?

Current theoretical thinking about dual processes in recognition relies heavily on the measurement operations embodied within the process dissociation procedure. We critically evaluate the ability of this procedure to support this theoretical enterprise. We show that there are alternative processes that would produce a rough invariance in familiarity (a key prediction of the dual-processing approach) and that the process dissociation procedure does not have the power to differentiate between these alternative possibilities. We also show that attempts to relate parameters estimated by the process dissociation procedure to subjective reports (remember-know judgments) cannot differentiate between alternative dual-processing models and that there are problems with some of the historical evidence and with obtaining converging evidence. Our conclusion is that more specific theories incorporating ideas about representation and process are required.

A twin study of psychometric intelligence and efficiency of information processing

Intelligence (IQ) can be seen as the efficiency of mental processes or cognition, as can basic information processing (IP) tasks like those used in our ongoing Memory, Attention and Problem Solving (MAPS) study. Measures of IQ and IP are correlated and both have a genetic component, so we are studying how the genetic variance in IQ is related to the genetic variance in IP. We measured intelligence with five subscales of the Multidimensional Aptitude Battery (MAB). The IP tasks included four variants of choice reaction time (CRT) and a visual inspection time (IT). The influence of genetic factors on the variances in each of the IQ, IP, and IT tasks was investigated in 250 identical and nonidentical twin pairs aged 16 years. For a subset of 50 pairs we have test–retest data that allow us to estimate the stability of the measures. MX was used for a multivariate genetic analysis that addresses whether the variance in IQ and IP measures is possibly mediated by common genetic factors. Analyses that show the modeled genetic and environmental influences on these measures of cognitive efficiency will be presented and their relevance to ideas on intelligence will be discussed.

The relationship between radiation-induced chemical processes and transverse relaxation times in polymer gel dosimeters

The effects of ionizing radiation in different compositions of polymer gel dosimeters are investigated using FT-Raman spectroscopy and NMR T-2 relaxation times. The dosimeters are manufactured from different concentrations of comonomers (acrylamide and N,N'-methylene-bis-acrylamide) dispersed in different concentrations of an aqueous gelatin matrix. Results are analysed using a model of fast exchange of magnetization between three proton pools. The fraction of protons in each pool is determined using the known chemical composition of the dosimeter and FT-Raman spectroscopy. Based on these results, the physical and chemical processes in interplay in the dosimeters are examined in view of their effect on the changes in T-2 The precipitation of growing macroradicals and the scavenging of free radicals by gelatin are used to explain the rate of polymerization. The model describes the changes in T-2 as a function of the absorbed dose up to 50 Gy for the different compositions. This is expected to aid the theoretical design of new, more efficient dosimeters, since it was demonstrated that the optimum dosimeter (i.e, with the lowest dose resolution) must have a range of relaxation times which match the range of T-2 values which can be determined with the lowest uncertainty using an MRI scanner.

Movement-related potentials in Huntington's disease: movement preparation and execution

Movement-related potentials (MRPs) reflect increasing cortical activity related to the preparation and execution of voluntary movement. Execution and preparatory components may be separated by comparing MRPs recorded from actual and imagined movement. Imagined movement initiates preparatory processes, but not motor execution activity. MRPs are maximal over the supplementary motor area (SMA), an area of the cortex involved in the planning and preparation of movement. The SMA receives input from the basal ganglia, which are affected in Huntington's disease (HD), a hyperkinetic movement disorder. In order to further elucidate the effects of the disorder upon the cortical activity relating to movement, MRPs were recorded from ten HD patients, and ten age-matched controls, whilst they performed and imagined performing a sequential button-pressing task. HD patients produced MRPs of significantly reduced size both for performed and imagined movement. The component relating to movement execution was obtained by subtracting the MRP for imagined movement from the MRP for performed movement, and was found to be normal in HD. The movement preparation component was found by subtracting the MRP found for a control condition of watching the visual cues from the MRP for imagined movement. This preparation component in HD was reduced in early slope, peak amplitude, and post-peak slope. This study therefore reported abnormal MRPs in HD. particularly in terms of the components relating to movement preparation, and this finding may further explain the movement deficits reported in the disease.

Developing qualitative career assessment processes

Assessment has been integral to career counseling since the early 1900s. During that time, the greatest amount of attention was focused on quantitative assessment. Thus, there is still very little to guide the development and conduct of qualitative assessment in career counseling. The authors present an overview of qualitative career assessment and its theoretical underpinnings and propose suggestions that could guide the development of qualitative career assessment instruments.

Visual biology of Hawaiian coral reef fishes. II. Colors of Hawaiian coral reef fish

The colors of 51 species of Hawaiian reef fish have been measured using a spectrometer and therefore can be described in objective terms that are not influenced by the human visual experience. In common with other known reef fish populations, the colors of Hawaiian reef fish occupy spectral positions from 300-800nm; yellow or orange with blue, yellow with black, and black with white are the most frequently combined colors; and there is no link between possession of ultraviolet (UV) reflectance and UV visual sensitivity or the potential for UV visual sensitivity. In contrast to other reef systems, blue, yellow, and orange appear more frequently in Hawaiian reef fish. Based on spectral quality of reflections from fish skin, trends in fish colors can be seen that are indicative of both visually driven selective pressures and chemical or physical constraints on the design of colors. UV-reflecting colors can function as semiprivate communication signals. White or yellow with black form highly contrasting patterns that transmit well through clear water. Labroid fishes display uniquely complex colors but lack the ability to see the UV component that is common in their pigments. Step-shaped spectral curves are usually long-wavelength colors such as yellow or red, and colors with a peak-shaped spectral curves are green, blue, violet, and UV.

Mental rotation processes in mathematically gifted boys: An fMRI investigation

The functional brain organisation of mathematically gifted adolescents may be different from those of average mathematical ability. In this study we used fMRI to examine the neural circuitry that mediates the performance of mathematically gifted boys and average ability controls while engaged in mental rotation. Eight math gifted male adolescents and five average ability male adolescents were presented 18 control and 18 mental rotation trials in two separate blocks. Participants selected one of four test stimuli to match the target stimulus by pressing one of four fibreoptic buttons. The control task required a simple 'best match' for the target stimulus. EPI scans were acquired on a 3-T MR scanner and a fixed effects statistical analysis (SPM99) was used to identify areas of significant activation in the rotation tasks, for the two groups. The results indicate that during mental rotation both groups activate the parietal lobes bilaterally, though to different levels. Moreover, the math gifted are uniformly bilateral in their pattern of activation, and engage some anterior regions not found in those of average ability. These regions include bilateral prefrontal cortex and the right anterior cingulate, which may serve to heighten concentration, and to optimise the pre-planning of purposeful actions.