Directional hearing is only weakly dependent on the rise time of acoustic stimuli.
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Acoustic Stimulation↗
Biomedical subjects
B Ronacher
Publications and source records attributed to B Ronacher.
Lateral optic flow does not influence distance estimation in the desert ant Cataglyphis fortis.
The present account answers the question of whether desert ants (Cataglyphis fortis) gauge the distance they have travelled by using self-induced lateral optic-flow parameters, as has been described for bees. The ants were trained to run to a distant food source within a channel whose walls were covered with black-and-white gratings. From the food source, they were transferred to test channels of double or half the training width, and the distance they travelled before searching for home and their walking speeds were recorded. Since the animals experience different motion parallax cues when walking in the broader or narrower channels, the optic-flow hypothesis predicted that the ants would walk faster and further in the broader channels, but more slowly and less far in the narrower channels. In contrast to this expectation, neither the walking speeds nor the searching distances depended on the width or height of the channels or on the pattern wavelengths. Even when ventral-field visual cues were excluded by covering the eyes with light-tight paint, the ants were not influenced by lateral optic flow-field cues. Hence, walking desert ants do not depend on self-induced visual flow-field cues in gauging the distance they have travelled, as do flying honeybees, but can measure locomotor distance exclusively by idiothetic means.
Animals↗
Analysis of common cold virus (human rhinovirus serotype 2) by capillary zone electrophoresis: the problem of peak identification.
Different preparations of human rhinovirus serotype 2 (HRV2), a common cold virus, were analyzed by capillary zone electrophoresis (CZE) in untreated fused-silica capillaries using borate buffer (100 mmol/L, pH 8.3) and sodium dodecyl sulfate (10 mmol/L) as additive to prevent wall adsorption. The electropherograms showed one major peak at 205- and 254-nm detection wavelengths. The identity of the peak as originating from native virus was confirmed by several indirect methods. Heating to 56 degrees C is known to lead to release of the genomic RNA from the viral capsid; this treatment resulted in the disappearance of the major peak and the emergence of a new predominant peak that was identified as RNA by enzymatic digestion. As expected, RNase treatment of the unheated sample remained without effect as the viral genome is inaccessible in the native viral shell. A monoclonal, virus-aggregating antibody was used for immunodepletion of native virus; again, the major peak disappeared upon removal of viral aggregates by centrifugation prior to CZE analysis. In combination, these results allowed for the unambiguous identification of the main peak as native HRV2 and of the minor peaks as contaminants present in various amounts in the different viral preparations. It is demonstrated that CZE allows for an extremely easy and rapid assessment of conformational state and purity of virions in a given viral preparation.
Electrolytes↗
Recombinant soluble low-density lipoprotein receptor fragment inhibits common cold infection.
A fragment of the human low-density lipoprotein receptor encompassing the seven ligand-binding repeats fused to a C-terminal oligo-His tag was expressed in Sf9 insect cells. The melittin signal sequence encoded in the baculovirus vector led to secretion of the protein into the cell supernatant in a soluble form. The receptor fragment bound its natural ligand beta-migrating very-low-density lipoprotein and human rhinovirus serotype 2 in non-reducing ligand blots. Infection of all minor group human rhinovirus serotypes investigated was inhibited by the presence of the receptor fragment during viral challenge of HeLa cells. Infection is inhibited by aggregation of the virions.
Animals↗
Recombinant soluble low density lipoprotein receptor fragment inhibits minor group rhinovirus infection in vitro.
A fragment of the low density lipoprotein receptor encompassing the seven ligand binding repeats was expressed in Sf9 insect cells as a fusion protein with a carboxyl-terminally linked hexa-his tag by using a baculovirus vector. Up to 10 mg/l of the fusion protein was secreted into the medium. The material was soluble in the absence of detergent and active in binding beta very low density lipoprotein and a member of the minor group of human rhinoviruses (HRV2) in ligand blots from sodium dodecyl sulfate-polyacrylamide gels run under nonreducing conditions. The receptor fragment specifically inhibits viral infection of HeLa cells by minor group HRVs in a concentration-dependent manner. Viral infectivity is neutralized by aggregation.
Animals↗
Pattern recognition in honeybees: multidimensional scaling reveals a city-block metric.
Bees were trained to discriminate ring-patterns which varied in number of rings and in size. Transfer-tests revealed size discrimination to be largely independent of pattern type and vice versa. A multidimensional scaling procedure, using Minkowski metrics as models, was applied in order to determine the bee's "perceptual metric". The city-block metric, and not the Euclidean metric, provided the best description of the data. Apparently, the bee's perceptual system derives the overall dissimilarity of complex ring-patterns additively from the component differences. These results are discussed with regard to "holistic" and "analytic" processing modes postulated for the perception of human subjects.
Animals↗
Perception of size and lightness of human observers: two criteria for holistic and analytic processing show no correlation in individuals.
Results of a triad-classification task and a multidimensional-scaling (MDS) experiment are compared for individual observers. Both paradigms are designed to reveal whether stimuli are perceived in a holistic or analytic manner (Garner 1974). Subjects differed substantially and consistently in their triad classification pattern. The majority of subjects selected stimuli according to dimensional criteria; this classification type is thought to indicate an analytic stimulus processing. Approximately one third of subjects, however, used a classification according to overall similarity (indicating holistic processing). Except for the very first session, virtually no intermediate classification occurred. This clear separation into two classification types suggests that there actually exist two strongly preferred processing modes. Intraindividual variability between sessions in general was small. In one case, however, a spontaneous switching from a purely dimensional classification to a purely similarity classification occurred. This indicates that the observers have different processing options at their disposal, and are not forced to use a particular processing mode by the stimulus type--as has been supposed in the original concept of integrality/separability of stimuli (Garner 1974). In the MDS experiment also substantial interindividual differences in the "best-fitting" Minkowski metric were found, indicating different processing types. However, for individuals participating in both experiments, there was no correlation between the results of the two experimental paradigms. This is interpreted as a result of the subject's ability to choose between a few perceptual-processing options.
Central Nervous System↗
Human pattern recognition: individually different strategies in analyzing complex stimuli.
Multidimensional scaling experiments were performed with "size" and "brightness" as parameters. Subjects (ss) had to rate the dissimilarity of pairs of discs differing in size or in brightness only, or in both parameters. It was then attempted to find a rule, by which the dissimilarity judgements of two-dimensional differences can be predicted from judgements given for the one-dimensional components. Minkowski-metrics were chosen as models, since for most of the ss the prerequisites for applying these metrics seem to be fulfilled. A simple procedure is described by which the one metric out of all Minkowski-metrics can be found which gives the best description for the data of a subject (Fig. 4). Although the task and the parameters used were the same for all ss, individually best metrics differed considerably, indicating individually different modes of perceptual analysis: Most ss adhered, roughly, to either the City-block or the Euclidean metric (cf. Fig. 10). (Only City-block metric was to be expected, since "size" and "brightness" are generally thought to be "separable" parameters.) In addition, there were three ss with metrics clearly different from both the City-block and the Euclidean metric (best exponents around 1.4). In view of those substantial differences between individuals one has to be cautious against the practice of averaging data from different ss.
Cybernetics↗
Spike synchronization of tympanic receptor fibres in a grasshopper (Chorthippus biguttulus L., Acrididae). A possible mechanism for detection of short gaps in model songs.
In recordings from single tympanic receptor fibres in C. biguttulus, the response to synthesized sounds (rectangularly modulated white noise) interrupted by very brief (a few milliseconds) gaps was examined. In behavioral tests, females of the species respond very differently to such 'model syllables' at moderate intensities, depending on the gap width. If the gaps (in a moderate-intensity syllable) are larger than 2 ms, the stimulus fails to elicit a response, whereas stimuli with gaps smaller than 1 ms are as effective as uninterrupted syllables (D. von Helversen 1972; O. von Helversen 1979). Neither the mean spike count nor the interspike-interval distribution of the single receptor response contains the information sufficient to distinguish uninterrupted syllables from syllables with gaps. On the other hand, examination of the temporal distribution of the spikes reveals that gaps (or the pulse onsets following the gaps) cause spike synchronization. An index of synchronization (IS) was defined as a measure of this gap-induced effect. Analysis of the receptor responses based on IS revealed differences that correspond quantitatively to the abrupt abolition of the behavioral response at a gap-width between 1 and 2 ms. From the hypothesis that such brief gaps are detected by the nervous system by way of spike synchronization in the tympanic nerve, one can predict certain features of the behavioral response to high-intensity stimuli. The gap-induced spike synchronization was more pronounced at higher temperatures. This effect was demonstrated in both summated recordings from the tympanic nerve and single fibre recordings. Experiments with primary auditory fibres of Locusta migratoria showed that the receptors in this species respond very similarly to the same stimuli. That is, the receptors of C. biguttulus are not specially adapted for detecting very brief gaps. Synchronization of the spikes in parallel receptor fibres of the tympanal nerve is probably a general feature of acridids; we infer that in C. biguttulus this gap-induced synchronized activity is detected by special processing in higher auditory centres.
Animal Communication↗
Human pattern recognition: evidence for a switching between strategies in analyzing complex stimuli.
In a preceding multidimensional scaling experiment, with "size" and "brightness" as parameters, subjects were found to use individually different strategies in processing compound stimuli: Most subjects adhered to either the Euclidean or the City-block metric (Ronacher and Bautz, 1985). In the experiment reported here, participants of the previous study were induced - by a manipulative instruction - to modify their strategy. With 5 out of 10 subjects a switching to another strategy occurred, which manifested itself in a drastic shift of the respective best metric (e.g. from Euclidean to City-block or vice versa). The extent and speed of changes as well as - in some instances - the stability of estimation accuracy show that subjects were not forced by the instruction to develop a new strategy. Results rather suggest that adult subjects have easily available two, or perhaps even more, alternative processing modes, the decision for one of them being a matter of a subject's preferences rather than of individually different abilities.
Cognition↗