Patrick W. Nye

An investigation of the mechanisms of eye movement control.

SummaryFeedback mechanisms exist in all the periferal sense organs including the eye, which acts as a highly efficient position control servo system. Histological studies so far have not revealed the precise circuitry of the eye movement control system but some information about it can be obtained by a study of the sources of feedback. Existing theories have considered three types of feedback originating in the oculomotor tract, in the proprioceptive fibres of the extrinsic eye muscles and from retinal image displacement. In the present experiments an optical arrangement has been used to vary or eliminate the amount of information available from retinal image motion, and the response of the eye to simple harmonic displacement of a target has been recorded. The response curves of gain (eyeball movement divided by target motion) against frequency indicate that the system is lion linear when the image falls in the retinal region which is insensitive to position. Outside this area, retinal image position is used as negative feedback but the information from the oculomotor tract must be regenerative. There is also evidence for feedback proportional to the first derivative of eyeball position and this function is ascribed to the proprioceptive signals; this form of feedback appears to saturate for large amplitude movements, thus avoiding heavy damping of the flick movements.A schematic eye movement control system having the same characteristics as the eye is proposed. The transfer function of this system indicates that it should be unstable if the sign of the retinal image feedback loop is reversed. Experiments with this form of feedback show that steady fixation is impossible and the eye performs a pendular nystagmus.

Application of MRI to the analysis of speech production

Computer models of the process of speech articulation require a detailed knowledge of the vocal tract configurations employed in speech and the application of acoustic theory to calculate the sound waveform. Almost all currently available data on vocal tract dimensions come from x-ray films and are severely limited in quantity and coherence due to restrictions on radiation dosage and intersubject differences. We are using MRI techniques to obtain the pharyngeal dimensions of speakers producing sustained vowels. The fact that MRI does not employ ionizing radiation provides speech research with the opportunity to obtain comprehensive bodies of much-needed data on the articulatory characteristics of single subjects.

The monocular eye movements of the pigeon

Abstract The monocular eye movements of both restrained and partially restrained pigeons have been measured by means of a mirror attached to the edge of the cornea. The principal observations may be summarized under the following categories. Flicks, or eye movements which bring about a rapid change of fixation, are found to occur only in response to sudden and unexpected motion of a visual stimulus and are rarely observed under the quiescent conditions of a darkened room. Drifts, which are slower movements of the eye between fixation points, occur at velocities of about 1–5 deg per sec and are stimulated by object motion. Tremor motion is of extremely low amplitude and is unlikely to serve any visual function. Oscillations occur in short bursts at frequencies of about 30 Hz and amplitudes of several degrees. The evidence indicates that this eye movement is normally executed during a blink and it is probable that it performs a polishing action on the cornea in conjunction with the nictitating membrane. The observations lead to the conclusion that although the range of rotational motion available to the pigeon is less than in man, it nevertheless possesses a well developed and precisely controlled oculomotor system which appears in some respects to out-perform our own.

Shadowing latency and imitation: the effect of familiarity with the phonetic patterning of English

Abstract Speakers imitate the speech they shadow. However, speech is not wholly imitative; speakers use their own speech habits or language knowledge in shadowing as well. We examined the interplay between the effects of input variables and of knowledge of the language on shadowing. We asked speakers to shadow utterances composed of phonetic sequences that varied in their order of approximation to English. Shadowing latency and errors reduced as order of approximation increased. This is consistent with the inference that knowledge of the language (e.g., speech habits, lexical or phonotactic knowledge) guides shadowing. To assess the interplay between this knowledge and the effect of imitation of the input on shadowing, we asked whether imitative fidelity varied with order of approximation. We used an AXB test in which X was a shadowed utterance, A (or B) was a shadowed response to X and B (or A) was a read version of the same utterance produced by the speaker of A (or B). Listeners were asked which of A or B was a better imitation of X. Generally, they chose the shadowed utterance; however, they did so significantly more frequently when the utterance was a 1st than a 12th order of approximation to English.

The binocular acuity of the pigeon measured in terms of the modulation transfer function

Abstract When comparing the performance of a birds eye with that of a man the use of such measures of acuity as the minimum resolrable separation between two points or two straight lines does not provide enough information about the full capability of the eye. The conclusions arrived at by these measures are liable to be misleading, particularly when such factors as the difference in overall receptor distribution in the retina, as distinct from that in a localised region, and the degree of mobility and stability of the eyes are ignored. Behavioral methods have been used to measure the binocular acuity of the pigeon in terms of the Modulation Transfer Function (MTF). This technique utilises targets subtending several degrees and, by avoiding many of the difficulties associated with determining accurate fixation, has permitted a more comprehensive comparison of visual performance with the results of human observers.

Voice register in Suai (Kuai): an analysis of perceptual and acoustic data.

Analyses of the perceptual and acoustic characteristics of the Register 1 (ʼclearʼ) versus Register 2 (ʼbreathyʼ) distinction have been carried out on the Kuai dialect of Suai, a Mon-Khmer language. The perception results were obtained from five-parameter synthesized stimuli. They showed that the primary parameter underlying the distinction is the frequency of onset of laryngeal excitation (F0). One other parameter making a significant contribution was the open quotient. The F0 result was confirmed by an acoustic analysis of eight pairs of natural utterances produced by native speakers. We conclude that the Suai language is in a state of flux with respect to the voice registers, although the distinction has not disappeared. The perceptual data reveal mixed levels of sensitivity, and the production data indicate that some speakers maintain a fairly good distinction, while others do not. The language seems to be replacing the register distinction with a prosodic one of pitch accent, possibly as a stage leading to tonogenesis.

Vowel height and the perception of consonantal nasality

By means of an articulatory synthesizer, the perception of the oral-nasal distinction in consonants was explored experimentally. This distinction was chosen because it is achieved by a very simple articulatory maneuver and because it is phonologically relevant in virtually every language. Lowering the velum in equal increments provided continua of CV syllables varying in size of velopharyngeal port which were divided perceptually into /d/ and /n/ categories by American English listeners. To test the hypothesis that the coarticulation of these nasal consonants with lower (more open) vowels requires a larger area of velopharyngeal coupling to give a nasal consonant precept, three oral-nasal continua incorporating the vowels /i/, /delta/, and /alpha/, respectively, were presented for identification. The results were compared with those of A. S. House and K. N. Stevens [J. Speech Hear. Disord. 21, 218-232 (1956)] and A. S. House [J. Speech Hear. Disord. 22, 190-204 (1957)] obtained with steady-state vowels and consonantal murmurs and with those of M. H. L. Hecker [J. Acoust. Soc. Am. 34, 179-188 (1962)]. Three conclusions emerged. First, the relationship between vowel height and the amount of velopharyngeal coupling needed for a nasal precept occurs in conditions where subjects are required to make linguistically relevant judgments. Second, the relationship can arise in conditions where vocalic coarticulation is present. Third, the relationship is not confined to vowels but can also be observed in the case of dynamically articulated consonants. One of the continua was also used for discrimination experiments, which yielded the classical pattern of high discriminability at the category boundary.

The dynamics of inhibitory interaction in a frog receptive field: A paradigm of paracontrast

Abstract Neurons in the frog retina, that generate on responses when the central regions of their receptive fields are stimulated and that are inhibited by a peripheral light, have been illuminated with a central and peripheral stimulus in varying time sequence. If a light is allowed to fall on the periphery of a receptive field as much as 160 msec after the onset of the central stimulus, the number of impulses produced by a cell is reduced. The time course of the interaction can be recorded in detail and indicates a possible physiological site for the psychophysical phenomenon of para-contrast.

An examination of the electroretinogram of the pigeon in response to stimuli of different intensity and wavelength and following intense chromatic adaptation

Abstract The photopic electroretinogram from cone-populated eyes contains a series of small wavelets found in both the on - and off-responses . Studies of these wavelets in the human ERG have indicated that the amplitude of individual peaks can be modified by varying spectral stimulation. These results, when considered together with observations of subjective color phenomena, suggest the hypothesis that the wavelet peaks are composed of a series of b -wavelets, arising from mechanisms associated with different classes of cones and distinguished from one another by different response latencies. Experiments on the visual system of the pigeon have confirmed that the wavelets originate in the retina, but measurements of their amplitudes and latencies do not support the b -wavelet hypothesis. Some features of the data, however, fit more closely the hypothesis that the wavelets are the results of a retinal oscillation.

The effects of retinal image motion in a simple pattern recognition task

SummaryThe recognition of misalignment in a pair of lines positioned end-to-end, as when setting a vernier scale, presents a simple problem in the detection of self-congruence. The accuracy with which this task can be performed has been measured both in normal vision and in the absence of retinal image motion; it is found that in the latter case the precision of the setting is decreased when the gap between the ends of the lines is small, but that the reduction in accuracy is not significant when the separation of the lines is increased to 30 min. arc. A search has been made for eye movements generating patterns of scanning activity designed to test the self-congruence of the vernier lines but without success, the distribution of spontaneous eye movements appears to be a function of the subject and not of the target lie is viewing.The reduction of vernier acuity in stabilized vision indicates that when retinal image motion is absent, the resultant pattern of neural activity is less well defined, this is ascribed to the loss of dynamic lateral inhibition effects but the reduction which occurs as the gap between the lines increases can be attributed to random neural events becoming confused with the stimulus; this hypothesis has been tested by the introduction of visual “noise” which is also found to reduce acuity.