Age dynamics of visually guided behavior and visual evoked potentials of altricial nestlings

Comparative study has been carried out of factors of organization of visually guided feeding behaviour (observation method) and the degree of maturity of the visual mechanisms by the criterion of Wulst EPs formation and of their recovery cycles in normally developing and visually deprived nestlings. In has been established that during the period following the opening of the eyes (5-9th day) the feeding behaviour is connected with diffuse photo-sensitivity of visual mechanisms. Diffuse photo-sensitivity fully provides for natural feeding behaviour at the corresponding stage of development of visual functions. Complete visual deprivation during the whole period of diffuse photo-sensitivity does not influence subsequent development of the visual system.     

Development of the auditory sensitivity and formation of the acoustically guided defensive behavior in nestlings of the pied flycatcher Ficedula hypoleuca

Age dynamics of generation of the evoked potentials (EP) in the field L of caudal nidopallium (the higher integrative center of the avian auditory system) and development of the auditory-guided defensive behavior were studied in control and visually deprived pied flycatcher Ficedula hypoleuca nestlings. It was shown that the rhythmically organized monofrequency signals with sound frequency 3.5 kHz and higher produced the defensive behavior as the auditory sensitivity to these frequencies matured. After 9 days, the species-specific alarm signal produced more effectively the defensive behavior than the tonal signals. The rhythmically organized sound with filling frequency 0.5 kHz, occupying the less low-frequency diapason than the feeding signal, produced the effect opposite to the alarm signal to increase the nestling mobility. At the initial stage of the defensive behavior development the auditory threshold fell markedly in the frequency diapason corresponding to the frequency diapason of the alarm signal (5–6 kHz), which seemed to facilitate involvement of this diapason signals in the defensive integration. The auditory EP generation thresholds in the whole studied diapason were lower in the visually deprived nestlings than in the normally developing one; however, the ability of the acoustic signals to suppress alimentary reactions fell significantly.     

Model of visually evoked cortical potentials

The pattern-reversal (P-VEPs) and the motion-onset (M-VEPs) of visual evoked potentials were modeled by means of three damped oscillators (O1, O2, O3) of identical construction. The O1, assumed to simulate the response of primary visual area (V1), was driven by the firing density of the lateral geniculate nuclei. 01 contributed mainly to the N75 and P100 peaks of the P-VEPs. The O2, driven by the O1 output, mimics the activity of V2, V3a, and MT. It contributed to the negative peak N145 of the P-VEPs or to the N160 in the M-VEPs. The O3 was suggested to model late slow processes probably of an attentive origin. The model parameters were set by optimization to follow the P-VEPs and M-VEPs obtained as a grand average of four young volunteers (Pz - A2 lead). The evoked potentials were described with normalized root mean square error lower than 13%.     

Improvement and impairment of visually guided behavior through LTP- and LTD-like exposure-based visual learning

Cellular studies have focused on long-term potentiation (LTP) and long-term depression (LTD) to understand requirements for persistent changes in synaptic connections. Whereas LTP is induced through high-frequency intermittent stimulation, low-frequency stimulation evokes LTD. Because of the ubiquitous efficacy of these protocols, they are considered fundamental mechanisms underlying learning. Here we adapted LTP/LTD-like protocols to visual stimulation to alter human visually guided behavior. In a change-detection task, participants reported luminance changes against distracting orientation changes. Subsequently, they were exposed to passive visual high- or low-frequency stimulation of either the relevant luminance or irrelevant orientation feature. LTP-like high-frequency protocols using luminance improved ability to detect luminance changes, whereas low-frequency LTD-like stimulation impaired performance. In contrast, LTP-like exposure of the irrelevant orientation feature impaired performance, whereas LTD-like orientation stimulation improved it. LTP-like effects were present for 10 days, whereas LTD-like effects lasted for a shorter period of time. Our data demonstrate that instead of electrically stimulating synapses, selective behavioral changes are evoked in humans by using equivalently timed visual stimulation, suggesting that both LTD- and LTP-like protocols control human behavior but that the direction of changes is determined by the feature incorporated into the stimulation protocol.     

Clutch-size variation in the Pied Flycatcher Ficedula hypoleuca

Variation in clutch-size of the Pied Flycatcher Ficedula hypoleuca was studied simultaneously in relation to latitude, longitude, altitude, laying date and habitat, using data from 103 areas from north Africa to north Norway (latitudinal range about 3900 km). Clutch-size variation was significantly related to altitude and habitat, small clutches being laid at high altitude and in coniferous forests. In contrast to some earlier studies, latitudinal or longitudinal clutch-size trends were not found.     

Processing of visually presented verbal stimuli in evoked potentials

The ERPs to familiar, unfamiliar, and recently learned words were recorded in 20 right-handed students who have recently studied a course in sensory physiology during performance of two tasks. The first task consisted in processing of different types of words, the second task required recognition of terms from sensory physiology. In the first task, three types of words were presented to a subject: familiar words related and unrelated to a given category and unfamiliar words. Subjects had to press the appropriate button responding to the questions whether they considered the presented word be related to the given category and whether they were sure in their answer. In the second task, terms from recently studied physiological material were presented to the students who had to detect whether those terms were related or unrelated to the given sensory system. Significant differences between late ERP components were revealed by Student test for matched samples. In the first task, component N400 of the ERP to unfamiliar words was higher than that of the ERP to familiar words. It was also higher in ERPs to words unrelated to the given category than in ERPs to related words. However, this component did not differ between ERPs to well and poorly acquired words in the test on sensory physiology. On the contrary, the late positive component was more expressed in ERPs to familiar and better acquired words in both tasks. Brain mechanisms of processing of different types of words are discussed.     

The visual field and visually guided behavior in the zebra finch (Taeniopygia guttata)

Summary Measurements were made of the physical properties of the visual system of the zebra finch, a bird with laterally placed eyes. The use of the visual system in pecking and courtship behavior was examined. It was demonstrated that the optical axis and the fovea of the eye point in a direction about 62° from the sagittal axis of the head. The visual field of each eye covers about 170° in the horizontal plane. In the frontal region there is an overlap of about 30°–40° where the birds can see binocularly; caudally there is a gap in the visual field of 60°. The point of best binocular viewing is in the sagittal plane at 16.5° below the beak.Concerning movement detection, the upper threshold is 540°/s for the binocular (frontal) part of the visual field and about 1100°/s for the monocular (lateral) part. Most fixations before pecking occur monocularly. A preference for one eye during pecking was not detected. During the courtship song, a male bird directs its head towards the female. The results are discussed in comparison with findings in pigeons and chickens.     

Operative memory and evoked visual potentials

Changes in human EEG and event-related potentials to the complex color stimulus were studied during performance of three cognitive tasks: passive viewing, visual searching, and memorizing and storing of the stimulus in the operative memory. It was shown that involvement of memory mechanisms resulted in the alpha rhythm suppression in both occipital and frontal brain areas. It was also accompanied by a generation of the slow positive component in the evoked potential recorded in the frontal areas (in the occipital areas this wave was manifested as negative).     

Heterogeneous Maturation of Retina of the Pied Flycatcher Ficedula hypoleuca

A method is developed to determine the moment of establishment of functional maturity of cones by the appearance of their lipid droplet. Using this method, the process of differentiation of photoreceptor layer cells is traced and general regularities are elucidated of growth and maturation of the bifoveal retina of chicks of the pied flycatcher Ficedula hypoleuca. Development of retina occurs heterochronously; the first colored lipid droplets determining mature photoreceptors are photooptically revealed locally in the temporal retina area at the 5th day; at the 7th day, the lipid droplets appear within the limits of the central fovea; then the maturation wave moves from the temporal and central fovea towards periphery of retina. By the 14th day the entire area of retina turns out to be filled with mature photoreceptors. It is suggested that the predominant early maturation of photoreceptor cells of the temporal area is due to a necessity of the forestalling development of the retina parts providing the short-focus binocular vision that is the most important for establishment of chick alimentary behavior and start of hunting on their own after flight from the nest.     

Growth and mortality of nestling great tits (Parus major) and pied flycatchers (Ficedula hypoleuca) in a heavy metal pollution gradient

We studied nestling growth, growth abnormalities, mortality and breeding success of two hole-nesting passerines, the great tit (Parus major) and the pied fly-catcher (Ficedula hypoleuca), at 14 study sites around a copper smelter complex in Harjavalta, south-west Finland in 1991–1993. The main pollutants in the area are heavy metals and sulphuric oxides. Exposure of birds to heavy metals was shown by measuring their faecal concentrations. Copper, nickel and lead contents of nestling faeces were high near the factory and decreased with distance away from the pollution source. F. hypoleuca nestlings suffered high mortality very close to the factory complex, but did relatively well at all other sites. Breeding success of P. major was below background levels up to 3–4 km from the pollution source and nestlings grew poorly close to the factory. Growth abnormalities of legs and wings in F. hypoleuca nestlings were significantly more common near the factory than farther away. In contrast, F. hypoleuca nestlings grew equally well at all distances. The poor breeding success of F. hypoleuca close to the factory complex is probably related to the high amount of heavy metals in its diet, and low availability of calcium-rich food items may enhance this effect. We suggest that the poor breeding success of P. major is related to habitat changes that have taken place around the factory. The different responses of these two bird species are probably due to their different diet. Our results show convincingly that species-specific differences in response should be carefully considered when planning schemes for air pollution monitoring.     

Environmental and genetic variation in the haematocrit of fledgling pied flycatchers Ficedula hypoleuca

We exposed females of a highly placentotrophic viviparous scincid lizard (Pseudemoia pagenstecheri) to various environmental factors during pregnancy, and quantified the effects of these treatments on their offspring. The clear result was that the phenotypes of neonatal lizards can be substantially modified by the environment that their mother experiences during gestation. Restricting prey availability to the females reduced the size of their offspring. Limiting the females' basking opportunities delayed their seasonal timing of parturition, and modified body proportions (tail length relative to snout-vent length) of the neonates. More surprisingly, female lizards that were regularly exposed to the scent of sympatric lizard-eating snakes gave birth to offspring that were heavier, had unusually long tails relative to body length, and were highly sensitive to the odour of those snakes (as measured by tongue-flick responses). The neonates' antipredator responses were also modified by the experimental treatment to which their mother was exposed. The modifications in body mass, tail length and response to snake scent plausibly reduce the offspring's vulnerability to predatory snakes, and hence may constitute adaptive maternal manipulations of the neonatal phenotype. Received: 6 July 1998 / Accepted: 5 December 1998     

Geographic variation in breeding parameters of the Pied Flycatcher Ficedula hypoleuca

Variation in laying date, clutch-size and number of fledglings of the Pied Flycatcher Ficedula hypoleuca was studied in relation to altitude, habitat and latitude, using data from 99 breeding areas from 35̀ N to 70̀ N. Laying date significantly increased with altitude and showed a significant quadratic relationship with latitude, with the earliest values at about 50̀ N. This quadratic relationship shows the same pattern as the relationship between arrival time of adults on the breeding areas and latitude. Clutch-size variation was significantly related to altitude and habitat, small clutches being laid at high altitude and in coniferous forests. Number of fledglings was significantly affected by habitat type, with lower values in the coniferous than in the deciduous forest. Mean clutch-size and mean number of fledglings showed the same quadratic relationship with latitude. In contrast to some earlier studies, an increased clutch-size with latitude was found, mainly because of new data from areas in the southern part of the species' distribution.     

Objective measurements of visual acuity by visual evoked potentials

Electrophysiological measurements of the threshold spatial frequency were conducted in 26 healthy subjects by using visual evoked potentials with the purpose of objective determination of the visual acuity. For that we proposed a universal method of the visual stimulation and EEG processing (using ICA decomposition in particular) to minimize errors arising on account of individual differences in the visual system functioning. As a result, a correlation of 0.74 and a logarithmic dependence were obtained between spatial resolution measured by electrophysiological and psychophysical methods. The proposed methods of objective measurement of visual resolution has a high effectiveness, does not depend on specificity of individual EEG and domination of different channels in the visual system. Therefore it is possible to determinate objectively the visual acuity in humans independently of their responses.