Gaze Field Research Articles

Study to evaluate efficacy of midriatic-digital-images when screening retinal-complications in people living with HIV.

To determine efficacy of mydriatic-digital images (MDI) when screening retinal complications in people living with HIV, in this study, a consecutive series of 79 people living with HIV (PLHIV) were evaluated. Two series of MDI were taken: - macula and optic nerve - nine gaze fields, which findings were compared with those obtained by a retina specialist. Both examiners were unaware of each other's results. Average age was 32.2years old, predominantly male (75.9%). Most frequent complications were HIV retina microangiopathies (6.3%) and toxoplasmosis (5.1%), followed by Cytomegalovirus and neuro-retinitis, optic neuritis and vitreitis, each one with 1.3%. Sensitivity with two MDI was 92.8% (CI 95% 66.0-100.0) and with nine 100% (CI 95% 77.0-100.0) and specificity of 95.4% (CI 95% 87.0-99.0) for both series. The positive predictive value was 81.3 and 82.4%, and negative predictive value was 98.4 and 100% respectively. The strength of agreement was substantial for the two series with the retina specialist examination (Kappa index of 0.836 and 0.888 respectively). Mydriatic-digital-images appear to be an effective method to screen for HIV-related retinal-complications in a regional hospital in Perú.

Different cultures, different images: a comparison between historic conservation area destination image choices of Chinese and Western tourists

ABSTRACT Using three Hangzhou Grand Canal historic conservation areas as the gaze fields, this study delineates differences in the image choices of visitors from cross-cultural backgrounds. Analysis of tourist-generated content, including destination image (DI) dimensions and frequency, suggests that Chinese tourists prefer human attractions and experiencing neighborhood life, while Western tourists prefer natural scenery and participating in tourist activities. The research also spotlights the phenomenon of the ‘tourist gaze circulatory.’ Tourists’ differentiated pursuits and on-site tourism experiences can influence the projection of DI, and the altered DI will in turn affect subsequent tourists. Based on this notion, suggestions are made for the in-depth development of the Canal’s historic conservation areas, differentiated for the different gazes of Chinese and Western tourists; and for a guide to help Western tourists experience Chinese urban life and enrich their gaze objects, with a view to protecting and enhancing world cultural heritage.

Abstract WP97: A Novel Behavioral Neuroscore Survey Improves Characterization of Experimental Ischemic Stroke in Mice

Stroke remains the fifth leading cause of death in the U.S, highlighting a pressing need to improve the translatability of experimental stroke studies. To more reproducibly mimic clinical assessments in animal stroke models, we developed and tested a novel behavioral Neuroscore assessment designed to serve as an experimental analog to the National Institutes of Health Stroke Scale. Our Neuroscore measured discrepancies in visual, sensorimotor, and fatigue-related performances over five tasks while generating a numerical score ranging from zero to eleven (zero representing normal). Once administered, the resulting score was used as a predictor for determining the severity of stroke. The Neuroscore was designed and administered on C57Bl/6 mice. To mimic the NIH Stroke Scale, the Neuroscore used similar, but mouse-appropriate components over five-minute administrations: Level of Consciousness, Gaze and Visual Field, Sensory-Limb testing in response to stimuli, and a motor component assessed with Paralysis-Paw Hang tasks. Inter-rater reliability assessments were also performed. For this initial experiment, the MCAo model (tandem common carotid/middle cerebral artery occlusion model) was tested. Neuroscore effectively and significantly increased on post-stroke day (PSD) 1 after MCAo (N=36) compared to shams (N=25, p<0.001). Upon analyzing inter-rater reliability, a significant intraclass correlation coefficient of 0.707 was calculated (N=3, p<0.001). In conclusion, we developed a novel Neuroscore evaluation to mimic the NIH Stroke Scale for mice. The Neuroscore appropriately changed after experimental stroke, and significant reliability findings indicated similar scoring across experimenters. Future testing in other stroke models, as well as in rats is indicated to further evaluate this tool as a universal post-stroke translational assessment.

Evaluation of operator visibility in three different cabins type Far-East combine harvesters

The purpose of this study was to develop and evaluate a visibility evaluation system for the cabin type Far-East combine harvester. The human field of view has been classified into five levels (perceptive, effective, stable gaze, induced, and auxiliary) depending on the rotation of the human head and eye. The divider, reaper lever, gearshift, dashboard, and conveying component were considered as major viewpoints of the cabin type Far-East combine harvester. The visibility of the cabin type Far-East combine harvester was evaluated quantitatively using viewpoints and human field of view levels. The visibility evaluation system for the cabin type Far-East combine harvester consisted of a laser pointer, stepping motors to control the directions of the view, gyro sensors to measure horizontal and vertical angles, and I/O interface to acquire the signals. The visibility evaluation tests were conducted at different postures ('sitting straight', 'sitting with a 15° tilt', 'standing straight', and 'standing with a 15° tilt') for three cabin type Far-East combine harvesters. The LSD (least significant difference) multiple comparison tests showed that the visibilities of viewpoints differed significantly as the operator's posture changed. The results showed that the posture while standing with a 15° tilt provided the best visibility. The average visibility scores at sitting postures were 22.3 (straight) and 24.4 (15° tilt), and the scores at standing postures were 18.7 (straight) and 29.5 (15° tilt). Also, the average visibility scores were observed in order from highest to lowest as reaper lever (44.6), divider (28.7), dashboard (23.1), conveying part (12.2), and gearshift lever (10.1). Most viewpoints of the cabin type Far-East combine harvester were out of the stable gaze field of the view level. Modifications of the cabin type Far-East combine harvester design will be required to enhance the visibility during harvesting operation and to improve safety and convenience of farmers. Keywords: combine harvester, cabin, operator visibility, field of view, evaluation system, ergonomics, safety and comfort DOI: 10.3965/j.ijabe.20160904.1850 Citation: Lee D H, Kim Y J, Choi C H, Chung S O. Evaluation of operator visibility in three different cabins type Far-East combine harvesters. Int J Agric & Biol Eng, 2016; 9(4): 33－44.

Recurrent Antitopographic Inhibition Mediates Competitive Stimulus Selection in an Attention Network

Topographically organized neurons represent multiple stimuli within complex visual scenes and compete for subsequent processing in higher visual centers. The underlying neural mechanisms of this process have long been elusive. We investigate an experimentally constrained model of a midbrain structure: the optic tectum and the reciprocally connected nucleus isthmi. We show that a recurrent antitopographic inhibition mediates the competitive stimulus selection between distant sensory inputs in this visual pathway. This recurrent antitopographic inhibition is fundamentally different from surround inhibition in that it projects on all locations of its input layer, except to the locus from which it receives input. At a larger scale, the model shows how a focal top-down input from a forebrain region, the arcopallial gaze field, biases the competitive stimulus selection via the combined activation of a local excitation and the recurrent antitopographic inhibition. Our findings reveal circuit mechanisms of competitive stimulus selection and should motivate a search for anatomical implementations of these mechanisms in a range of vertebrate attentional systems.

Multimodal representation of optic flow in area PEc of macaque monkey

The visual perception of self-motion is mainly provided by optic flow. Eyes usually scan the environment during locomotion, and the gaze is not always directed to the focus of expansion (FOE) of the flow field. Such eye movements change the retinal FOE position with respect to the fovea. Here, we assess if optic flow selective neurons in parietal area PEc are modulated by eye position. We recorded single neuron activity during radial optic flow stimulation in two monkeys, varying eye and retinal FOE positions. We found that the majority of PEc neurons are modulated by the FOE retinotopic position with different tuning for expansion and contraction. Although many neurons did not show any gaze field without visual stimulation, the eye position modulated optic flow responses in about half of the cells. These novel results suggest that PEc neurons integrate both visual and eye position signals, and allow us to hypothesize their role in guiding locomotion as a part of a cortical network involved in FOE representation during self-motion. Visual and eye position interaction in this area could be seen as a contribution to the building of the invariant space representation necessary to motor planning.

캐빈형 콤바인의 시계성 평가에 관한 연구

The purpose of this study was to develop a visibility evaluation system for cabin type combine. Human's field of view was classified into five levels (perceptive, effective, stable gaze, induced, and auxiliary) depending on rotation of human's head and eye. Divider, reaper lever, gearshift, dashboard, and conveying part were considered as major viewpoints of combine. Visibilities of combine was evaluated quantitatively using the viewpoints and the human's field of view levels. The visibility evaluation system for cabin type combine was consisted of a laser pointer, stepping motors to control the direction of view, gyro sensors to measure horizontal and vertical angle, and I/O interface to acquire the signals. Tests were conducted with different postures ('sitting straight', 'sitting with <TEX>$15^{\circ}$</TEX> tilt', 'standing straight', and 'standing with <TEX>$15^{\circ}$</TEX> tilt'). The LSD (least significant difference) multiple comparison tests showed that the visibilities of viewpoints were different significantly as the operator's postures were changed. The results showed that the posture at standing with <TEX>$15^{\circ}$</TEX> tilt provided the best visibility for operators. The divider of the combine was invisible due to blocking with the cabin frame at many postures. The reaper lever showed good visibilities at the postures of sitting or standing with <TEX>$15^{\circ}$</TEX> tilt. The gearshift, the dashboard, and the conveying part had reasonable visibilities at the posture of sitting with <TEX>$15^{\circ}$</TEX> tilt. However, most viewpoints of the combine were out of the stable gaze field of view level. Modifications of the combine design will be required to enhance the visibility during harvesting operation for farmers' safety and convenience.

Binocular Vertical Rectus Muscle Recession For Comitant Vertical Strabismus

Binocular vertical rectus muscle recession has not been formally evaluated in the correction of comitant vertical strabismus. Eight patients with stable comitant vertical strabismus for at least 6 months were included. All underwent recession of the superior rectus muscle of the hypertropic eye combined with an equal or nearly equal recession of the inferior rectus muscle in the hypotropic eye. On the day before surgery, on one of the first three postoperative days, and at one year postoperatively, ocular alignment in vertical and horizontal gaze directions were measured with simultaneous and alternate cover test at a viewing distance of 5 meters, and with the two dimensional Hess screen test. The field of single binocular vision was determined with a Goldmann perimeter. The Lang stereopsis chart was presented at the last follow-up visit. All patients were orthotropic at the last postoperative follow-up visit. In primary gaze, the degree of vertical and horizontal phoria diminished significantly. Normal alignment was achieved in nearly all gaze directions and stereopsis was reestablished. The field of single binocular vision enlarged after the surgery. Binocular vertical rectus muscle recession is an effective surgical approach for patients with comitant vertical ocular misalignment.

Distinct Mechanisms for Top-Down Control of Neural Gain and Sensitivity in the Owl Optic Tectum

We demonstrate that distinct mechanisms of top-down control regulate, respectively, the sensitivity and gain of sensory responses in the owl's optic tectum (OT). Electrical microstimulation in the forebrain gaze control area, the arcopallial gaze field (AGF), results in a space-specific regulation of sensory responses in the OT. AGF microstimulation increases the responsiveness of OT neurons representing stimuli at the same location as that represented at the AGF site. We show that the mechanism that underlies this effect operates focally to enhance neuronal sensitivity and improve tuning consistency and spatial resolution. At the same time, AGF microstimulation decreases the responsiveness of OT neurons representing stimuli at all other locations. The mechanism that underlies this effect operates globally to modulate neuronal gain. The coordinated action of these different mechanisms can account for many of the reported effects of spatial attention on neural responses in monkeys and on behavioral performance in humans.

Stimulus-Specific Adaptations in the Gaze Control System of the Barn Owl

Abrupt orientation to novel stimuli is a critical, memory-dependent task performed by the brain. In the present study, we examined two gaze control centers of the barn owl: the optic tectum (OT) and the arcopallium gaze fields (AGFs). Responses of neurons to long sequences of dichotic sound bursts comprised of two sounds differing in the probability of appearance were analyzed. We report that auditory neurons in the OT and in the AGFs tend to respond stronger to rarely presented sounds (novel sounds) than to the same sounds when presented frequently. This history-dependent phenomenon, known as stimulus-specific adaptation (SSA), was demonstrated for rare sound frequencies, binaural localization cues [interaural time difference (ITD) and level difference (ILD)] and sound amplitudes. The manifestation of SSA in such a variety of independent acoustic features, in the midbrain and in the forebrain, supports the notion that SSA is involved in sensory memory and novelty detection. To track the origin of SSA, we analyzed responses of neurons in the external nucleus of the inferior colliculus (ICX; the source of auditory input to the OT) to similar sequences of sound bursts. Neurons in the ICX responded stronger to rare sound frequencies, but did not respond differently to rare ITDs, ILDs, or sound amplitudes. We hypothesize that part of the SSA reported here is computed in high-level networks, giving rise to novelty signals that modulate tectal responses in a context-dependent manner.

Top-Down Control of Multimodal Sensitivity in the Barn Owl Optic Tectum

We studied the effects of electrically microstimulating a gaze-control area in the owl's forebrain, the arcopallial gaze fields (AGFs), on the responsiveness of neurons in the optic tectum (OT) to visual and auditory stimuli. Microstimulation of the AGF enhanced the visual and auditory responsiveness and stimulus discriminability of OT neurons representing the same location in space as that represented at the microstimulation site in the AGF. At such OT sites, AGF microstimulation also sharpened auditory receptive fields and shifted them toward the location represented at the AGF stimulation site. At the same time, AGF microstimulation suppressed the responsiveness of OT neurons that represented visual or auditory stimuli at other locations in space. The top-down influences of this forebrain gaze-control area on sensory responsiveness in the owl OT are strikingly similar to the space-specific regulation of visual responsiveness in the monkey visual cortex produced by voluntary attention as well as by microstimulation of the frontal eye fields. This experimental approach provides a means for discovering mechanisms that underlie the top-down regulation of sensory responses.

Isolated Superior Oblique Tucking: An Effective Procedure for Superior Oblique Palsy with Profound Superior Oblique Underaction

To compare efficacy and complications of isolated unilateral superior oblique tucking in patients with unilateral superior oblique palsy (SOP). A retrospective analysis of 24 cases of unilateral SOP, 13 Acquired (group 1), and 11 Congenital (group 2), who underwent isolated unilateral superior oblique tuck over a 13-year period was performed. The mean preoperative vertical deviation in primary gaze was 10 +/- 3 PD for group 1 and 12 +/- 5 PD for group 2 and mean vertical deviation in lateral gaze of affected superior oblique was 19 +/- 5 PD for group 1 and 21 +/- 9 PD for group 2. The mean postoperative vertical deviation in primary gaze for group 1 after a mean follow-up period of 15 +/- 21 months was 1 +/- 3 PD; for group 2 after a mean follow-up period of 17 +/- 13 months was 2 +/- 3 PD, and in lateral gaze of affected superior oblique was 3 +/- 5 PD for group 1 and 5 +/- 6 PD for group 2. The mean correction of vertical deviation in primary gaze at last follow-up was 8 +/- 2 PD for group 1 and 9 +/- 5PD for group 2 ( P > 0.05) and in the lateral gaze field of affected superior oblique muscle was 16 +/- 4 PD for group 1 and 15 +/- 5 PD for group 2 ( P > 0.05). The mean preoperative torsion was 9 +/- 4 degrees for group 1 and 9 +/- 2 degrees for group 2; mean postoperative torsion was 1.2 +/- 2.2 degrees for group 1 and 1 +/- 1 degrees for group 2. The mean torsion corrected for group 1 was 8 +/- 3 degrees and for group 2 was 8 +/- 2 degrees ( P > 0.05). Only one patient in group 1 and three patients in group 2 required reoperation to correct residual deviation. A mild postoperative limitation to elevation in adduction was seen in all cases but was asymptomatic and lessened over time. Isolated unilateral superior oblique tucking corrected a large amount of the vertical deviation and torsion with minimal complications in selective patients of both congenital and acquired superior oblique palsy. Superior oblique tucking is a safe and effective procedure and can be considered in patients with SOP meeting selective criteria.

Early auditory experience induces frequency-specific, adaptive plasticity in the forebrain gaze fields of the barn owl.

Binaural acoustic cues such as interaural time and level differences (ITDs and ILDs) are used by many species to determine the locations of sound sources. The relationship between cue values and locations in space is frequency dependent and varies from individual to individual. In the current study, we tested the capacity of neurons in the forebrain localization pathway of the barn owl to adjust their tuning for binaural cues in a frequency-dependent manner in response to auditory experience. Auditory experience was altered by raising young owls with a passive acoustic filtering device that caused frequency-dependent changes in ITD and ILD. Extracellular recordings were made in normal and device-reared owls to characterize frequency-specific ITD and ILD tuning in the auditory archistriatum (AAr), an output structure of the forebrain localization pathway. In device-reared owls, individual sites in the AAr exhibited highly abnormal, frequency-dependent variations in ITD tuning, and across the population of sampled sites, there were frequency-dependent shifts in the representation of ITD. These changes were in a direction that compensated for the acoustic effects of the device on ITD and therefore tended to restore a normal representation of auditory space. Although ILD tuning was degraded relative to normal at many sites in the AAr of device-reared owls, the representation of frequency-specific ILDs across the population of sampled sites was shifted in the adaptive direction. These results demonstrate that early auditory experience shapes the representation of binaural cues in the forebrain localization pathway in an adaptive, frequency-dependent manner.

Early Visual Experience Shapes the Representation of Auditory Space in the Forebrain Gaze Fields of the Barn Owl

Auditory spatial information is processed in parallel forebrain and midbrain pathways. Sensory experience early in life has been shown to exert a powerful influence on the representation of auditory space in the midbrain space-processing pathway. The goal of this study was to determine whether early experience also shapes the representation of auditory space in the forebrain. Owls were raised wearing prismatic spectacles that shifted the visual field in the horizontal plane. This manipulation altered the relationship between interaural time differences (ITDs), the principal cue used for azimuthal localization, and locations of auditory stimuli in the visual field. Extracellular recordings were used to characterize ITD tuning in the auditory archistriatum (AAr), a subdivision of the forebrain gaze fields, in normal and prism-reared owls. Prism rearing altered the representation of ITD in the AAr. In prism-reared owls, unit tuning for ITD was shifted in the adaptive direction, according to the direction of the optical displacement imposed by the spectacles. Changes in ITD tuning involved the acquisition of unit responses to adaptive ITD values and, to a lesser extent, the elimination of responses to nonadaptive (previously normal) ITD values. Shifts in ITD tuning in the AAr were similar to shifts in ITD tuning observed in the optic tectum of the same owls. This experience-based adjustment of binaural tuning in the AAr helps to maintain mutual registry between the forebrain and midbrain representations of auditory space and may help to ensure consistent behavioral responses to auditory stimuli.

Encoding of Smooth Pursuit Direction and Eye Position by Neurons of Area MSTd of Macaque Monkey

The spike activity of neurons was recorded from the dorsal bank of the superior temporal sulcus (area MSTd) of alert behaving macaque monkeys performing visual fixation or target tracking tasks, with the aim of studying the tuning features of these neurons with both the direction of slow eye movement and the position of gaze. One hundred thirty-two neurons were tested for several fixation points and tracking directions. Many of them (43%) tuned to the direction of pursuit, regardless of the angle of gaze. Some (18%) showed a tonic discharge modulated by the static position of the eyes without pursuit direction specificity. A substantial number of cells (22%) were characterized by a discharge rate tuned to pursuit direction but influenced also by angle of gaze. Tuning curves for eye movement direction presented an average bandwidth of 130 degrees and turned out to be continuously overlapping, suggesting a sort of vector coding of smooth pursuit direction. Gaze fields of eye position (EP) neurons were mostly ramp-like, with center of ramps shifted away from the straight ahead, implying a form of scalar coding of gaze eccentricity. The different categories of cells were intermingled and close to each other, suggesting possible reciprocal interactions within the same cortical area. These results show that EP and pursuit direction are signaled mainly by separate neuronal elements in area MSTd. Moreover, some cells can integrate both signals. Taking into account the visual responses of MSTd neurons to large, textured, moving fields, it is suggested that this area could be the site of interaction between visuo-oculomotor signals related to visual motion detection, slow eye movement direction, and EP. This signal interaction may be important for integrative functions such as analysis of external or self-induced visual motion, cortical control of pursuit eye movements, and eye/head coordination.

Eye position-dependent activation of neurones in striate cortex of macaque.

Extracellular recordings were made in the striate cortex in awake, behaving monkeys to test the influence of the eye position on cellular activity. Two monkeys (Macaca mulatta) were trained to fixate a small spot at 25 different eye positions. About half (52%) of the studied neurones showed a selective gaze field (GF). The cells' activities increased significantly when the monkey fixated at this field of view. For the majority of these neurones, GFs were located at the contralateral field of view with respect to the hemisphere from which responses were recorded, and were usually found a few degrees peripheral to the related receptive field. Eye position-dependent neurones were found at different depths of cortex, but mostly in the superficial layers. The results indicate that some neurones in striate cortex may code information about eye position and could contribute to target localization in a head-centred coordinate system by combining retinal and afferent eye position signals.

Gaze field properties of eye position neurones in areas MST and 7a of the macaque monkey

The activity of parietal cortex neurones primarily related to eye position (EP neurones) was studied in macaque monkeys with the aim of precisely defining the neurones' gaze fields (GF) and comparing them in two functionally different areas, MSTd and 7a. Discharge rates of single neurones in the inferior parietal lobule and in the underlying cortex of the superior temporal sulcus were recorded in two Java monkeys while the animals fixated a steady visual target positioned at several different points on a video screen. The GFs were then drawn as a regression surface fitting the mean discharge rates. Cells tonically influenced by the angle of gaze were found in both areas. The GFs most often took the form of a nearly planar surface best characterized as a ramp tilted towards a hemifield or quadrant of the visual field, shifted eccentrically with respect to the straight ahead (primary position), and with a midpoint centred between 0 deg and 20 deg of gaze eccentricity and saturation between 10 deg and 35 deg. In a minority of cases, the discharge rate was nearly maximal at the primary position and decreased to a minimum within 35 deg of eccentricity. In other instances, the GFs were peaked surfaces, limited to a restricted part of visual space. EP neurones, while showing similar gaze fields in areas MST and 7a, were found intermingled with functionally different types of cells. The results suggest that EP neurones similar to those already described in several areas of the monkey parietal cortex are present also in area MST. These cells, by signalling the degree of gaze eccentricity from the primary position, encode gaze position in an orbito-centered frame extending up to 30-35 deg from the straight-ahead. The role of EP neurones might be to supply contiguous elements with a gaze eccentricity signal required for visuo-motor processes such as the control of tracking movements.

Contribution of the forebrain archistriatal gaze fields to auditory orienting behavior in the barn owl

A region in the barn owl forebrain, referred to as the archistriatal gaze fields (AGF), is shown to be involved in auditory orienting behavior. In a previous study, electrical microstimulation of the AGF was shown to produce saccadic movements of the eyes and head, and anatomical data revealed that neurons in the AGF region of the archistriatum project directly to brainstem tegmental nuclei that mediate gaze changes. In this study, we investigated the effects of AGF inactivation on the auditory orienting responses of trained barn owls. The AGF and/or the optic tectum (OT) were inactivated pharmacologically using the GABAA agonist muscimol. Inactivation of the AGF alone had no effect on the probability or accuracy of orienting responses to contralateral acoustic stimuli. Inactivation of the OT alone decreased the probability of responses to contralateral stimuli, but the animals were still capable of orienting accurately toward stimuli on about 60% of the trials. Inactivation of both the AGF and the OT drastically decreased the probability of responses to 16-21% and, on the few trials that the animals did respond, there was no relationship between the final direction of gaze and the location of the stimulus. Thus, with the AGF and OT both inactivated, the animals were no longer capable of orienting accurately toward acoustic stimuli located on the contralateral side. These data confirm that the AGF is involved in gaze control and that the AGF and the OT have parallel access to gaze control circuitry in the brainstem tegmentum. In these respects, the AGF in barn owls is functionally equivalent to the frontal eye fields in primates.

Characterization of a forebrain gaze field in the archistriatum of the barn owl: microstimulation and anatomical connections

We present evidence that the archistriatum in the forebrain of the barn owl participates in gaze control, that it can mediate gaze changes independently of the optic tectum (OT), and that it projects in parallel to both the OT and to saccade-generating circuitry in the brainstem tegmentum. These properties are similar to those of the frontal eye fields (FEF) in the prefrontal cortex of primates. The forebrain was surveyed for sites where electrical microstimulation would induce head saccades. Head (and eye) saccades were elicited from the anterior 70% of the archistriatum, a region that we refer to as the archistriatal gaze fields (AGF). At single stimulation sites in the AGF, saccade amplitude tended to vary as a function of stimulation parameters (current strength, pulse frequency, and train duration) and starting head position. In contrast, saccade direction was largely independent of these parameters. Saccade direction did vary over a wide range of primarily contraversive directions with the site of stimulation in the AGF. Using anatomical pathway tracing techniques, we found that the archistriatum projects strongly and in parallel to the deep layers of the OT and to nuclei in the midline brainstem tegmentum. Previous work has shown that electrical microstimulation of either of these brainstem regions evokes saccadic movements of the head and/or eyes (du Lac and Knudsen, 1990; Masino and Knudsen, 1992b). Inactivation of the OT with lidocaine reduced the size but did not eliminate (or change the direction of) the saccades evoked by AGF stimulation. The direct anatomical pathway from the archistriatum to the midline tegmental nuclei can account for saccades that persist following OT inactivation. The similarities between the AGF in barn owls and the FEF in primates suggest that the same general plan of anatomical and functional organization supports the contribution of the forebrain to gaze control in a wide variety of species.

Binaural tuning of auditory units in the forebrain archistriatal gaze fields of the barn owl: local organization but no space map

We identified a region in the archistriatum of the barn owl forebrain that contains neurons sensitive to auditory stimuli. Nearly all of these neurons are tuned for binaural localization cues. The archistriatum is known to be the primary source of motor-related output from the avian forebrain and, in barn owls, contributes to the control of gaze, much like the frontal eye fields in monkeys. The auditory region is located in the medial portion of the archistriatum, at the level of the anterior commissure, and is within the region of the archistriatum from which head saccades can be elicited by electrical microstimulation (see preceding companion article, Knudsen et al., 1995). Free-field measurements revealed that auditory sites have large, spatial receptive fields. However, within these large receptive fields, responses are tuned sharply for sound source location. Dichotic measurements showed that auditory sites are tuned broadly for frequency and that the majority are tuned to particular values of interaural time differences and interaural level differences, the principal cues used by barn owls for sound localization. The tuning of sites to these binaural cues is essentially independent of sound level. The auditory properties of units in the medial archistriatum are similar to those of units in the optic tectum, a structure that also contributes to gaze control. Unlike the optic tectum, however, the auditory region of the archistriatum does not contain a single, continuous auditory map of space. Instead, it is organized into dorsoventral clusters of sites with similar binaural (spatial) tuning. The different representations of auditory space in closely related structures in the forebrain (archistriatum) and midbrain (optic tectum) probably reflect the fact that the forebrain contributes to a wide variety of sensorimotor tasks more complicated than gaze control.