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Biomedical subjects

B J Frost

Publications and source records attributed to B J Frost.

At least 37 records · Page 2Linked to original sources
PubMed1993

Factors affecting the onset and magnitude of linear vection.

The role of central and peripheral vision in the production of linear vection was assessed by using displays in which flow structure and sources of internal and external depth information were manipulated. Radial optical flow was more effective for inducing self-motion in both central and peripheral visual fields than was lamellar flow in displays of the same size. The presence of external occlusion information was necessary to induce linear vection when small displays were composed of lamellar flow, whereas the effectiveness of small radial displays did not depend on the availability of occlusion edges.

Adolescent↗
PubMed1992

Time to collision is signalled by neurons in the nucleus rotundus of pigeons.

Throughout the animal kingdom, the sight of a rapidly approaching object usually signals danger and elicits an escape response. Gibson suggested that the symmetrical expansion of an object's image (looming) is the critical variable determining that the object is on a collision course with the observer. Similarly, large expanding flow-fields like those produced by locomotion may precipitate manoeuvres such as turning or landing. From such observations it has been shown that the optic flow parameter, tau, which specifies time to contact with the approaching object best fits the behavioural data. We describe a subpopulation of neurons in the nucleus rotundus of the pigeon brain that respond selectively to objects moving on a collision course towards the bird.

Animals↗
PubMed1992

Linear vection in the central visual field facilitated by kinetic depth cues.

Illusory self-motion (vection) is thought to be determined by motion in the peripheral visual field, whereas stimulation of more central retinal areas results in object-motion perception. Recent data suggest that vection can be produced by stimulation of the central visual field provided it is configured as a more distant surface. In this study vection strength (tracking speed, onset latency, and the percentage of trials where vection was experienced) and the direction of self-motion produced by displays moving in the central visual field were investigated. Apparent depth, introduced by using kinetic occlusion information, influenced vection strength. Central displays perceived to be in the background elicited stronger vection than identical displays appearing in the foreground. Further, increasing the eccentricity of these displays from the central retina diminished vection strength. If the central and peripheral displays were moved in opposite directions, vection strength was unaffected, and the direction of vection was determined by motion of the central display on almost half of the trials when the centre was far. Near centres produced fewer centre-consistent responses. A complete understanding of linear vection requires that factors such as display size, retinal locus, and apparent depth plane are considered.

Adult↗
PubMed1991

Visual response characteristics of neurons in the nucleus isthmi magnocellularis and nucleus isthmi parvocellularis of pigeons.

The visual response characteristics of single cells in the nucleus isthmi (NI) of pigeons were investigated using standard extracellular recording techniques. The results show that both major components of NI, the parvocellular NI (Ipc) and the magnocellular NI (Imc), have a tight retinotopic organization where nasal regions of the visual field are mapped onto the rostral poles of Ipc and Imc, and temporal regions of the visual field are mapped onto the caudal poles. The more ventral regions of these nuclei receive input from more inferior regions of visual space. The receptive fields (RFs) of both Ipc and Imc are large and oval-shaped, and their long axis is oriented vertically in the visual field. Most RFs are distributed on the contralateral visual horizon, and no binocular responses were found in either Ipc or Imc. All of the excitatory RFs of NI cells were surrounded by large inhibitory regions which participated in the dramatic modulation of the driven visual response when a large background pattern was moved across this zone. Although both Ipc and Imc neurons are driven best by small dark spots, some of them also show orientation selectivity to bars which may result from their oval-shaped RF (74% of Imc cells, 20/38, were orientation selective as compared to 10% of the Ipc cells, 3/30). It is suggested that some tectal cells with small RFs, and which originate from a vertically oriented zone may converge onto a single NI neuron to produce the elliptical shaped receptive fields.

Animals↗
PubMed1991

Purkinje cells in the vestibulocerebellum of the pigeon respond best to either translational or rotational wholefield visual motion.

Using standard extracellular techniques, the response properties of neurons in the vestibulocerebellum of the pigeon to movement of a wholefield visual stimulus were determined. Complex spike activity of Purkinje cells was modulated in a direction-selective manner by the stimulus and 94% of cells were binocularly driven. Some neurons preferred the same direction of wholefield motion in both eyes, simulating optic flow which results from self-translation, while others preferred the opposite direction in each eye, simulating optic flow resulting from rotation. Four functional classes of neurons were found: (1) Descent cells preferred upward motion in both eyes; (2) Ascent neurons preferred downward motion in both eyes; (3) Roll cells preferred upward and downward motion in the ipsilateral and contralateral eyes respectively; and (4) Yaw cells preferred forward (temporal to nasal) and backward motion in the ipsilateral and contralateral eyes respectively. The observation that these neurons clearly distinguish rotational and translational optic flow patterns suggest they may play an important role in controlling locomotor activities of the pigeon.

Animals↗
PubMed1990

The visual response properties of neurons in the nucleus of the basal optic root of the pigeon: a quantitative analysis.

The response characteristics of single-units in the nucleus of the basal optic root (nBOR) of the pigeon accessory optic system (AOS) were investigated using standard extracellular techniques. The receptive fields (RFs) were large (20-115 degrees long) and elliptical and were found throughout the contralateral visual field with the exception of the red field. The RFs did not have inhibitory surrounds and there was no evidence of retinotopic organization. Most neurons responded to small moving spots although the optimal stimulus was wholefield motion of a particular direction. Analysis of 166 single-units showed that neurons preferring upward, downward and backward (nasal to temporal) motion were equally abundant (32.5, 32.5 and 31% respectively), while less than 5% preferred forward (temporal to nasal) motion. Mapping studies demonstrated that UP units were located in the dorsal portion of the nucleus; DOWN units were found ventral to UP units; BACK units were found along the ventral surface of the nucleus; and FORWARD units were found in the posterior-dorsolateral margin of the nucleus. Most cells were excited by wholefield motion in the preferred direction and inhibited by motion approximately 180 degrees in the opposite direction, however, some cells lacked the excitatory component while other lacked the inhibitory component. Neurons were grouped into six categories based on the relative contributions of excitation and inhibition. These results are compared with investigations of the AOS of other vertebrates.

Animals↗
PubMed1990

The processing of object and self-motion in the tectofugal and accessory optic pathways of birds.

This paper reviews electrophysiological studies of motion processing in the tectofugal and accessory optic systems (AOS), and suggests these are specialized respectively for the analysis of object motion and self motion. Evidence is presented which shows that directionally specific neurons in the tectofugal system process local motion and are inhibited by wholefield motion. These cells respond to kinematograms and moving occlusion edges and may therefore also be involved in figure-ground segregation and depth perception. In contrast, cells in the nucleus of the basal optic root (nBOR), a component of the AOS, respond best to large slowly moving patterns. These cells are directionally selective preferring either upward, downward or backward directions. In the posterior region of the nBOR some cells have been found which are binocular and prefer either the same or opposite directions of motion in the two eyes. Thus, these cells are tuned to respond optimally to either translational or rotational components of wholefield motion and it is suggested these may be involved in the control of posture and locomotion.

Animals↗
PubMed1990

Retinotopic representation of the bifoveate eye of the kestrel (Falco spraverius) on the optic tectum.

Like many diurnal raptors, the American kestrel or sparrow hawk, Falco sparverius, possesses two foveae in each eye. In this study, we used fundus photography and reversed ophthalmoscopy to plot the projection of these foveae onto the visual field, together with other retinal landmarks such as the pecten and ora terminali. From such data, it was determined that the central monocular fovea (CMF) and temporal binocular fovea (TBF) were separated by 36 deg and that the kestrel has 58 deg of binocular overlap when the eyes are appropriately converged. Single-cell and multi-unit recordings were used to systematically explore the tectal surface and map receptive fields (RF) onto a hemispheric screen. A retinotopic map of the tectal surface was produced from such data and revealed an expanded representation for each fovea on the tectum and a systematic increase in RF size from fovea to periphery. The functional significance of this organization is discussed.

Animals↗
PubMed1990

Binocular neurons in the nucleus of the basal optic root (nBOR) of the pigeon are selective for either translational or rotational visual flow.

Previous electrophysiological studies have shown that neurons in the nucleus of the basal optic root (nBOR) of the pigeon respond best to wholefield stimuli moving slowly in a particular direction in the contralateral visual field. In this study, we have found that some nBOR neurons respond to wholefield stimulation of both eyes. These binocular neurons have spatially separate receptive fields in both visual fields. Some binocular neurons prefer the same direction of wholefield motion in both eyes, and thus respond best to wholefield visual motion which would result from translation movements of the bird, either ascent, descent, or forward and backward motion. Other neurons prefer opposite directions of wholefield motion in each eye and therefore respond optimally to wholefield visual motion simulating rotational movements of the bird, either roll or yaw. These binocular neurons may play a crucial part in the locomotor behavior of the pigeon by providing visual information distinguishing translational and rotational movements.

Animals↗
PubMed1990

Effect of orientation on visual and vibrotactile letter identification.

The effect of stimulus orientation of letters presented either visually or vibrotactually was examined to obtain basic information on sensory substitution using the tactile sense. The reaction time (RT) to identify the letters F and R presented in normal or mirror-image form at four orientations each was measured. In addition, conditions of 0 degree and 270 degrees of head rotation from vertical and arm rotation from the midline axis were employed. Data from 5 trained subjects showed that vibrotactile RTs were always longer than visual RTs. Stimulus rotation away from normal orientation increased visual RTs significantly but not vibrotactile RTs. Visual orientation effect then seemed to be determined by the body-coordinate system but not the vibrotactile orientation. Although further studies are warranted, from the results of this experiment, any convenient and constant stimulus orientation could be used with a wearable vibrotactile display system to exploit passive touch.

Attention↗
PubMed1989

Functional activity in the accessory optic system during visual, vestibular and visual-vestibular stimulation in the pigeon.

(14C) 2-deoxyglucose (2-DG) autoradiography was used to examine functional activity in the pigeon accessory optic system (AOS) during visual, vestibular and combined visual-vestibular stimulation. Monocular horizontal whole-field visual stimulation resulted in preferential labelling of the contralateral nucleus of the basal optic root (nBOR), in medial and lateral, but not dorsal regions, as well as the contralateral nucleus lentiformis mesencephali pars magnocellularis (LMmc). Increased activation was also observed bilaterally in LMmc after vestibular stimulation alone. 2-DG accumulation was maximal during combined visual-vestibular stimulation in both nBOR and LMmc.

Animals↗
PubMed1988

Deep tectal cells in pigeons respond to kinematograms.

Deep tectal neurons in pigeons respond selectively to moving visual stimuli, and are inhibited by large background patterns moved in-phase with these stimuli. In this investigation we demonstrate that these same deep tectal neurons respond equally well to kinematograms as they do to traditional luminance contrast stimuli typically employed in visual experiments. Computer generated kinematograms, the motion domain equivalents of random dot stereograms, were used as stimuli in these experiments. These kinematograms, where a small centrally located set of random dots is moved coherently in one direction while the remaining dots are moved in a different direction, thus constitute a pure motion stimulus where the stimulus form is only visible in the dynamic pattern, but does not exist on any single frame. Both 'object' configured and 'hole' configured kinematograms were employed; the former appearing as regions of texture moving over, or in front of, the background texture, while the latter appear as windows through which a more distant textured surface is revealed. Extracellular recordings from isolated deep tectal cells showed that all units responded in a very similar manner whether the stimulus was an 'object' configured kinematogram or the more traditional luminance contrast variety. This similarity included directional selectivity, the in-phase inhibition anti-phase facilitation effect, and sensitivity to opposed motion independent of direction. However, when the kinematograms were configured as 'holes' none of the units tested responded to these stimuli. The significance of these observations for tectal functioning, image segmentation through motion and animal camouflage is discussed.

Animals↗
PubMed1987

Word and feature identification by profoundly deaf teenagers using the Queen's University tactile vocoder.

The experiments described are part of an ongoing evaluation of the Queen's University Tactile Vocoder, a device that allows the acoustic waveform to be felt as a vibrational pattern on the skin. Two prelingually profoundly deaf teenagers reached criterion on a 50-word vocabulary (live voice, single speaker) using information obtained solely from the tactile vocoder with 28.5 and 24.0 hours of training. Immediately following word-learning experiments, subjects were asked to place 16 CVs into five phonemic categories (voiced & unvoiced stops, voiced & unvoiced fricatives, approximants). Average accuracy was 84.5%. Similar performance (89.6%) was obtained for placement of 12 VCs into four phonemic categories. Subjects were able to acquire some general rules about voicing and manner of articulation cues.

Adolescent↗
PubMed1986

Cerebral and local cerebral metabolism in the cat during slow wave and REM sleep.

[14C]2-deoxyglucose autoradiography was used to show cerebral and regional cerebral metabolism during slow-wave sleep (SWS) and rapid-eye-movement sleep (REM) in the cat. Lower levels of mean cerebral metabolism, reflecting cerebral energy conservation, were associated with SWS. A clear link between REM and mean cerebral metabolism was not observed. At the regional level, SWS was associated with markedly low metabolism in thalamic sensory relays and in cortex. REM was associated with relatively low metabolism in the cerebellum, but with relatively high metabolism in the hippocampus, and in some 'motor' regions including the trigeminal and red nuclei. Thus, SWS was linked to cerebral energy conservation and to particularly low levels of functional activity in cortical and sub-cortical sensory regions. REM was unlike SWS in that: REM did not appear to be strongly linked to cerebral energy conservation; REM was linked to metabolism in fewer brain regions than was SWS; and most REM-linked regions exhibited relatively high levels of metabolism. In addition, while SWS was most clearly associated with functional activity in sensory regions, REM was linked to functional activity in a small number of limbic and motor regions. In sum, SWS and REM are associated with distinctive cerebral metabolic and functional states.

Animals↗
PubMed1986

Continuing evaluation of the Queen's University tactile vocoder. I: Identification of open set words.

Identification of open set words, by an experienced normal hearing subject using the tactile vocoder developed at Queen's University, was examined. The tactile vocoder filters and processes the acoustic waveform into 16 filter channels, each of which controls a vibrator on the skin surface. After acquiring a 250-word vocabulary through the tactile vocoder, the subject was presented with three sets of 1000 different open set words in three reception conditions. The percentages of words correctly identified in the tactile vocoder (TV), lipreading (L), and lipreading plus tactile vocoder (L + TV) conditions were 8.8, 39.4, and 68.7 percent respectively. Phonemic analysis of stimulus/response pairs revealed that 36.7, 64.9 and 85.5 percent of the phonemes were correctly identified in TV, L, and L + TV conditions, respectively, indicating that incorrect-response words often contained many correct phonemes. Also, syllabic stress of stimulus and response words was identical 88 percent of the time in the TV condition. Important information about speech was transmitted through the tactile vocoder.

Deafness↗
PubMed1986

Continuing evaluation of the Queen's University tactile vocoder II: Identification of open set sentences and tracking narrative.

Identification of open set words by an experienced normal hearing subject using the tactile vocoder developed at Queen's University was examined. The tactile vocoder filters and processes the acoustic waveform into 16 filter channels each of which activates a vibrator on the skin surface. After acquiring a 250-word vocabulary through the tactile vocoder, the subject was presented with 1000 different open set sentences in two reception conditions. The percentages of words correctly identified within the sentences in the lipreading (L) and lipreading plus tactile vocoder (L + TV) conditions were 57.8 percent and 79.6 percent, respectively. After two presentations of the stimulus sentences, the number of sentences repeated verbatim in the L + TV condition was 58.4 percent, which was 27.8 percent higher than scores obtained in the L condition. Performance on the tactile vocoder was also evaluated using the "tracking procedure," in which phrases of text are read to the subject who attempts to repeat the material verbatim. The final tracking rate obtained using lipreading was 15.3 words per minute, which was considerably lower than the L + TV tracking rate of 49.3 words per minute. The tactile vocoder provided valuable information which improved the subject's lipreading ability.

Evaluation Studies as Topic↗
PubMed1985

Intracortical facilitation among co-oriented, co-axially aligned simple cells in cat striate cortex.

Most neurons in cat striate visual cortex show inhibitory effects when moving contours are presented beyond the limits of classic receptive field regions. Facilitatory effects are also present in about 40% of simple cells. Here, we report a highly specific form of this facilitation, mediated only by neurons possessing both an orientation tuning matched to the test unit, and a receptive field position aligned with its long axis. This finding illustrates one of the intracortical interconnection schemes hypothesized by Mitchison and Crick (1982). Periodic clustering in long, intrinsic axons may signify a neuron seeking specific functional interactions like these across columnar systems in both the spatial and orientation domains.

Animals↗