Specific Ensembles Research Articles

Empirical orthogonal function representations of stochastic sound-speed ensembles

The representation of stochastic ensembles of sound-speed profiles by convenient and efficient means is examined. The procedure is based on using discrete empirical orthogonal functions (EOFs) with random coefficients. The eventual objective is to use the EOF representations in random wave propagation models, for which their efficiency is expected to reduce significantly the computational expense. To illustrate the procedure, two specific model ensembles are considered. The first consists of deep-water (Munk) sound-speed profiles, and the second has shallow-water profiles obtained from temperature profiles generated by a portion of the generalized digital environmental model (GDEM). After a statistical distribution of stochastic environmental input parameters is assumed, EOFs are calculated for ensembles of up to 10 000 profile samples. Relations between the statistics of the input parameters and the sound speed profiles that are obtained from EOF representations are investigated. In each case examined, the number of EOFs needed to account for virtually all of the sample variance is at most four. Additional cases are considered using Continental Shelf data by assuming measured profiles represent ensemble samples. [Work supported by ONR.]

Some principles in the brain analysis of important signals: mapping and stimulus recognition.

This essay addresses two questions: What are the meanings of different kinds of brain maps? Can the recognition of important communicative signals and other stimuli known to the system be adequately explained by an ensemble code? Several kinds and grades of brain maps are distinguished. Before we can properly state the meaning, especially of the higher forms of multiple and multifactor maps, we need to learn where they project. At the higher levels this is a labor-intensive task, requiring also ingenuity and ethological thinking to devise stimuli. The neuronal basis of recognition in those cases where behavior or perception is triggered in an either-or manner has chiefly been attributed to one or the other of two classes of models: a large spatiotemporal configuration of many kinds of cells in which there is little convergence of input, and a small set of nearly equivalent cells after successive convergences. The latter is known to exist but it is not clear how far it goes or for what classes of stimuli. The former is a more popular view but carries several burdens in required assumptions and is essentially not demonstrable or disprovable. I believe both exist and operate in sequence: specific ensembles are inputs to small sets of equivalent recognition units and specific arrays of different recognition units at higher and higher levels of abstraction may constitute the specific configurations for the most sophisticated recognitions. Our information base is pitifully small, especially in comparative physiology of higher integrative functions of the brain and in comparative behaviour.

Phase‐dependent sensitivity to perturbation reveals the nature of speech coordinative structures

The detailed workings of hypothesized speech coordinative structures‐functionally specific articulator ensembles—can be explored by varying the phase of an unexpected perturbation during ongoing speech. The present research examined the characteristics of remote (nonmechanically linked) and autogenic compensation when the lower lip was perturbed in either the opening or closing phase of the motion for the utterance /bæb/. Preliminary results indicate that the relative contribution of remote and autogenic responses to the perturbation varies with the phase of perturbation; remote compensation plays a greater role when the lower lip is perturbed during the closing phase of motion for a bilabial consonant. Analysis of trials immediately following perturbed trials reveals a hysteresis in the articulator configuration due to the preceding loaded trials. The articulators tend to overcompensate in these trials in a manner that reflects the phase sensitivity of the immediate compensation pattern. These phase‐sensitive compensation patterns provide strong support for the notion that the articulators in speech are flexibly assembled as coordinative structures for accomplishing specific phonetic goals. [Work supported by NINCDS and NSERC.]

Nonlinear analysis with an arbitrary stimulus ensemble

A family of Wiener-type methods is discussed in a general context. These methods share the concept of expansion of an unknown transducer as an orthogonal series. The terms of the series are drawn from a hierarchy of subspaces of transducers that are orthogonal with respect to a particular stimulus ensemble. Choices of specific stochastic ensembles lead to previously described analytical methods, including the classical one of Wiener.

THE FLAVONOIDS OF THE DECIDUOUS RHODODENDRON OF NORTH AMERICA (ERICACEAE)

The native Azaleas of North America (Rhododendron: subgenus Pentanthera) produce 58 flavonoids in five aglycone classes: flavonols, dihydroflavonols, flavanones, dihydrochalcones and chalcones. A comparison of the flavonoids of selected samples of these species indicated that the compounds generally occur as species specific ensembles. Species were grouped into “alliances” based on common flavonoid constituents and a phylogenetic treatment of the group was developed. Evolutionary trends of flavonoids within subgenus Pentanthera are not well‐defined but appear to be associated with a loss of the ability to synthesize some compounds and a decrease in diversity of glycosides and methoxylated flavonoids. Intraspecific variation in flavonoids was found in Rhododendron canescens, R. alabamense and R. austrinum when these were sampled on a population basis.

The different connections and motor outputs of lateral and medial giant fibres in the crayfish.

ABSTRACT High-speed cinematography was used to analyse the abdominal movements of crayfish in response to separate stimulation of medial and lateral giant axons. These films showed that the medial giant fibres command complete abdominal flexions with little flaring of the tail appendages. The lateral giants, in contrast, evoked a relatively weak flexion of the middle abdominal segments, accompanied by promotion of the exopodites of the uropods. An examination of the muscles activated by the two types of giant fibres shows that differences in the connexions between the giant fibres and specific motor neurones can account for the behavioural differences observed. The output of the giant fibres was determined in the sixth abdominal ganglion, where their differential effects are most pronounced. The medial giants activate motor neurones whose axons emerge from root 6 of the sixth ganglion. The lateral giants activate motor neurones whose axons emerge via roots 2 and 3, as well as those emerging via root 6. The larger motor neurones associated with the giant axons in the sixth root of the sixth ganglion have been mapped by Procion Yellow injection, and the terminations of the central giant axons in the sixth ganglion have also been determined. The connexions revealed by this technique are consistent with the physiological findings. The evidence suggests that root 6 of the sixth ganglion is homologous with root 3 of the more anterior ganglia. However, the giant motor neurone of the sixth ganglion has not been identified. The medial and lateral giant fibres, and perhaps other specific ‘command’ interneurones, can thus drive specific ensembles of phasic motor neurones to provide a range of stereotyped quick movements. In this respect the organization of the phasic system of interneurones and motor neurones resembles that in the tonic system.