Visual space from visual motion: turn integration in tethered flying Drosophila

Organisms navigating by path integration need to continuously measure their forward movement and their angular orientation with respect to an external reference. How they do it is little understood. Tethered flies at the flight simulator "navigate" in an artificial visual landscape without forward movement. They can return to a previously held orientation if the panorama provides a singularity (landmark) as reference. Surprisingly, in a regularly striped drum without singularities, they can use a temporal cue instead. In this experiment the arena is illuminated with only one color that is either green or blue. The arena is virtually divided into four quadrants. Whenever a quadrant boundary moves past an arbitrary point, the color of the arena light changes. When a fly is heated with one color it acquires a preference for the other one. Subsequently, it avoids the borders toward the potentially 'hot' quadrants even without touching them. The only way to achieve this is by turn integration, that is, by adding and subtracting all the turns it performs once it crosses the border. The color switch defining the border crossing resets the turn integrator, using the orientation of the arena at this moment as reference. In contrast, landmarks or, if it were available, the skylight compass enable the fly to establish by pattern learning any orientation as a reference. If the reference orientation coincides with the desired orientation, that is, if the animal stores the pattern while being oriented toward the goal, it can maintain its orientation without recourse to turn integration (which may be error prone).     

Heart rate-Qt interval relationship during postural change and exercise. A possible connection to cardiac contractility

The QT interval of the electrocardiogram, although often coordinated in an inverse relationship to heart rate, appears from the existing evidence to be regulated by mechanisms separate from those that govern heart rate. The purpose of this inquiry was to explore further the relationship of the two and to test other factors that may contribute to the regulation of QT. Heart rate and QT duration were measured in healthy human subjects during postural change and exercise. The data showed that, while coordinated in an inverse relationship under some circumstances, under others heart rate and QT were discordant, leading to the inference that there is no fixed linkage between the two. Previous work by the authors and other published studies have suggested that ventricular contractility may have more predictable association with QT shortening than do increases in heart rate. Observations of force of ventricular contraction (HI and IJ velocity) as reflected in ballisto-cardiographic tracings were made using each of 12 human subjects as the authors' own control. The data revealed a highly significant correlation between the velocity measures and QT duration (p less than 0.01) but not heart rate. These findings led to the conclusion that there is clearly not a fixed relationship between heart rate and QT interval and to the hypothesis that QT may more closely reflect the degree of cardiac contractility.     

Heart rate—QT interval relationship during postural change and exercise

The QT interval of the electrocardiogram, although often coordinated in an inverse relationship to heart rate, appears from the existing evidence to be regulated by mechanisms separate from those that govern heart rate. The purpose of this inquiry was to explore further the relationship of the two and to test other factors that may contribute to the regulation of QT. Heart rate and QT duration were measured in healthy human subjects during postural change and exercise. The data showed that, while coordinated in an inverse relationship under some circumstances, under others heart rate and QT were discordant, leading to the inference that there is no fixed linkage between the two. Previous work by the authors and other published studies have suggested that ventricular contractility may have more predictable association with QT shortening than do increases in heart rate. Observations of force of ventricular contraction (HI and IJ velocity) as reflected in ballisto-cardiographic tracings were made using each of 12 human subjects as the authors’ own control. The data revealed a highly significant correlation between the velocity measures and QT duration (p<0.01) but not heart rate. These findings led to the conclusion that there is clearly not a fixed relationship between heart rate and QT interval and to the hypothesis that QT may more closely reflect the degree of cardiac contractility.     

Motion parallax judgements of depth as a function of the direction and type of head movement

We compared the relative effectiveness of rotating or translating the head, either horizontally or vertically, on the perception of depth resulting from motion parallax. Using Rogers and Graham's (1979) paradigm, we yoked the movement of random dots on a screen to movements of the head, simulating a corrugated surface. In two experiments, subjects nulled the apparent depth or motion seen in the display. Horizontal head movements yielded the most precise depth judgements, irrespective of whether the head translated or rotated. Motion thresholds were higher than those for depth and were independent of direction of head movement. In a third experiment, suprathreshold stimuli that simulated differing amounts of depth were used, and the subjects' perception of depth was virtually the same for all types and directions of head movement. In our stimulus situation, rotating or translating the head either vertically or horizontally produced motion parallax cues for depth that were equally effective. Our results also showed that, within a range, retinal image motion from head movement is converted into a depth signal and that above that range location constancy breaks down and motion is seen.     

The voice of confidence: Paralinguistic cues and audience evaluation

A standard speaker read linguistically confident and doubtful texts in a confident or doubtful voice. A computer-based acoustic analysis of the four tapes showed that paralinguistic confidence was expressed by increased loudness of voice, rapid rate of speech, and infrequent, short pauses. Under some conditions, higher pitch levels and greater pitch and energy fluctuations in the voice were related to paralinguistic confidence. In a 2 × 2 design, observers perceived and used these cues to attribute confidence and related personality traits to the speaker. Both text and voice cues are related to confidence ratings; in addition, the two types of cue are related to differing personality attributes.     

Rhythmic heart rate variability (sinus arrhythmia) related to stages of sleep

Evidence that the excursion of rhythmic heart rate variability (sinus arrhythmia) may be manipulated by altering the subject’s state of concentration, prompted a study of effects associated with different stages of sleep. There were 9 healthy subjects, ages 16–69, and one 55-year-old subject (C.P.) with a myocardial infarction history. Awake and during sleep the excursion of heart rate variability was greatest among the younger subjects, decreasing progressively with age. C.P. displayed rhythmic heart rate variability only when asleep. In light sleep (Stages 1 and 2) all subjects, with the exception of the 69-year-old, whose rate remained almost fixed throughout the night, displayed rhythmic heart rate variability, roughly synchronous with respiration. Neither the elderly subjeot nor C.P. entered into deep sleep (Stages 3 and 4). Among the other subjects, deep sleep was marked by a precise correlation between the frequency of respiration and heart rate variability. In REM sleep, however, in all subjects, there was often a total dissociation between respiration and rhythmic heart rate variability. There were periods of no heart rate variability with continuing regular respiration and of rhythmic heart rate variability with spontaneous breath holding. In the presence of heart rate variability during REM, C.P. displayed frequent ectopic beats, but ectopic beats were nearly absent in REM periods characterized by a steady, unvarying heart rate. The range of heart rate variability at rest and during sleep (sinus arrhythmia) reflects the manner in which autonomic activity is brought to bear in regulating the heart beat. The study of the behavior of sinus arrhythmia may offer a way to anticipate the occurrence of dangerous cardiac dysarrhythmias and sudden death, especially during sleep.