Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Meridians”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33Linked to original sources
PubMed1997

The central visual field in homonymous hemianopia. Evidence for unilateral foveal representation.

BACKGROUND: Controversy exists regarding the cortical representation of the foveal region in man. The most plausible explanation for foveal sparing in homonymous hemianopia is dual blood supply to the occipital pole. However, bilateral cortical representation has also been suggested. OBJECTIVE: To determine the representation of the foveal region in the primary human visual cortex. DESIGN: A case series correlating magnetic resonance imaging to the visual field defects of 6 patients with occipital lobe injuries. RESULTS: Four patients with foveal-sparing hemianopic defects demonstrated unilateral sparing of the posterior occipital cortex. In contrast, 2 patients with central homonymous defects showed isolated involvement of the posterior pole. One patient also demonstrated 5 degrees of field sparing along the horizontal meridian. CONCLUSIONS: On the basis of correlating the findings of magnetic resonance imaging and visual field defects in patients with occipital lobe injury, we conclude that the foveal region is unilaterally represented in the primary human visual cortex and that a major portion of the striate cortex is dedicated to the central 10 degrees of vision. The horizontal meridian of the visual field is represented deep within the calcarine banks at the fissure base.

Adult↗
PubMed2003

Refractive error and ethnicity in children.

OBJECTIVE: To report the baseline prevalence of refractive error in the study population. DESIGN: A multicenter, longitudinal, observational study of refractive error and ocular development in children from 4 ethnic groups. PATIENTS AND METHODS: The study population included 2523 children (534 African American, 491 Asian, 463 Hispanic, and 1035 white) in grades 1 to 8 (age, 5-17 years). Myopia was defined as -0.75 diopters (D) or more and hyperopia as +1.25 D or more in each principal meridian, and astigmatism was defined as at least a 1.00-D difference between the 2 principal meridians (cycloplegic autorefraction). RESULTS: Overall, 9.2% of the children were myopic, 12.8% were hyperopic, and 28.4% were astigmatic. There were significant differences in the refractive error prevalences as a function of ethnicity (chi2, P<.001), even after controlling for age and sex (polychotomous logistic regression, P<.001). For myopia, Asians had the highest prevalence (18.5%), followed by Hispanics (13.2%). Whites had the lowest prevalence of myopia (4.4%), which was not significantly different from African Americans (6.6%). For hyperopia, whites had the highest prevalence (19.3%), followed by Hispanics (12.7%). Asians had the lowest prevalence of hyperopia (6.3%) and were not significantly different from African Americans (6.4%). For astigmatism, Asians and Hispanics had the highest prevalences (33.6% and 36.9%, respectively) and did not differ from each other (P =.17). African Americans had the lowest prevalence of astigmatism (20.0%), followed by whites (26.4%). CONCLUSION: There were significant differences in the prevalence of refractive errors among ethnic groups, even after controlling for age and sex (P<.001).

Adolescent↗
PubMed1980

Surgical correction of high postkeratoplasty astigmatism. Relaxing incisions vs wedge resection.

Improved techniques and procedures have resulted in a higher rate of clear grafts after penetrating keratoplasty. A clear graft, however, does not give a good visual result if high corneal astigmatism prevents the successful wearing of spectacles or contact lenses. This article describes the methods and results of two microsurgical techniques--the corneal wedge resection to steepen the flat meridian and relaxing incisions to flatten the steep meridian. Average reduction in corneal astigmatism was greater for the wedge resection (ten cases) (6.50 diopters as compared with 4.25 D [16 cases] for the relaxing incisions). The relaxing incisions operation was successful in 75% of cases with stabilization of corneal curvature readings in an average of three weeks and is an outpatient procedure. After a wedge resection, corneal stabilization usually takes months. We believe that wedge resection should be reserved for cases in which relaxing incisions are unsuccessful.

Astigmatism↗
PubMed1984

Static perimetry in chloroquine retinopathy. Perifoveal patterns of visual field depression.

Results of threshold static perimetry in nine cases of toxic retinopathy produced by chloroquine phosphate and hydroxychloroquine sulfate are reported. Pericentral visual field defects in an advanced case correlated well with ophthalmoscopically visible defects in the pigment epithelium. In a less advanced case, perifoveal defects in the visual field of one eye were found to be demonstrable in the absence of any fundus abnormalities by either ophthalmoscopy or fluorescein angiography. In both cases, visual field defects were deepest on the superior or vertical meridian, just above the point of fixation. Since defects were found to be deepest along the superior vertical meridian, threshold static perimetry that includes this location should be the most sensitive method of detecting the early stages of visual field damage in chloroquine retinopathy.

Adult↗
PubMed1988

Paired arcuate keratotomy. A surgical approach to mixed and myopic astigmatism.

Twenty-five cadaver eyes were used to study the effect of paired arcuate keratotomy on corneal astigmatic changes. Paired arcuate incisions placed at optical zones of 5, 6, 7, 8, and 9 mm were progressively lengthened from 45 degrees to 60 degrees, 90 degrees, and, finally, 120 degrees. The corneal flattening in the meridian centered over the incisions and the corneal steepening 90 degrees away were quantified with each successive lengthening. Linear regression analysis showed a direct linear relationship of corneal astigmatic change (sum of corneal flattening and steepening, or delta K) to decreasing optical zone size as measured in millimeters and increasing incision length as measured in degrees. The delta K value ranged from 2.65 +/- 1.07 diopters to 22.05 +/- 3.55 D. The flattening/steepening coupling ratio mean was 1.47 +/- 0.41. Progressively longer paired arcuate incisions produced a predictable and titratable corneal flattening in the meridian centered over the incisions and a slightly smaller corneal steepening 90 degrees away, making the procedure ideal for mixed astigmatism.

Anthropometry↗
PubMed1991

Trapezoidal keratotomy for the correction of naturally occurring astigmatism.

We performed trapezoidal keratotomy, consisting of combined nonintersecting semiradial and transverse incisions, in 64 eyes of 45 consecutive patients with naturally occurring astigmatism. The central clear zone diameter and number and length of transverse incisions were determined by the refractive error. Mean preoperative refractive astigmatism was 3.18 +/- 1.16 diopters (D) (range, 2.25 to 7.00 D). At the 1-year follow-up examination, the mean surgically corrected astigmatism determined by vector analysis was 3.70 +/- 1.50 D (range, 0.75 to 8.5 D), and the mean residual refractive astigmatism was 0.85 +/- 0.72 D (range, 0 to 4.0 D), with 64% of eyes having 1.00 D or less. The smaller the clear zone diameter, the greater the astigmatic correction. Longer transverse incisions produced more steepening of the secondary meridian. The operative complications included microperforation (5%), misalignment of surgical meridian (6%), encroachment on clear zone (5%), and inadvertent crossed incisions (11%). Trapezoidal keratotomy reduced naturally occurring astigmatism, but with only fair predictability and with some irregular astigmatism due to irregular wound healing.

Adolescent↗
PubMed1997

The second visual area in the marmoset monkey: visuotopic organisation, magnification factors, architectonical boundaries, and modularity.

The organisation of the second visual area (V2) in marmoset monkeys was studied by means of extracellular recordings of responses to visual stimulation and examination of myelin- and cytochrome oxidase-stained sections. Area V2 forms a continuous cortical belt of variable width (1-2 mm adjacent to the foveal representation of V1, and 3-3.5 mm near the midline and on the tentorial surface) bordering V1 on the lateral, dorsal, medial, and tentorial surfaces of the occipital lobe. The total surface area of V2 is approximately 100 mm2, or about 50% of the surface area of V1 in the same individuals. In each hemisphere, the receptive fields of V2 neurones cover the entire contralateral visual hemifield, forming an ordered visuotopic representation. As in other simians, the dorsal and ventral halves of V2 represent the lower and upper contralateral quadrants, respectively, with little invasion of the ipsilateral hemifield. The representation of the vertical meridian forms the caudal border of V2, with V1, whereas a field discontinuity approximately coincident with the horizontal meridian forms the rostral border of V2, with other visually responsive areas. The bridge of cortex connecting dorsal and ventral V2 contains neurones with receptive fields centred within 1 degree of the centre of the fovea. The visuotopy, size, shape and location of V2 show little variation among individuals. Analysis of cortical magnification factor (CMF) revealed that the V2 map of the visual field is highly anisotropic: for any given eccentricity, the CMF is approximately twice as large in the dimension parallel to the V1/V2 border as it is perpendicular to this border. Moreover, comparison of V2 and V1 in the same individuals demonstrated that the representation of the central visual field is emphasised in V2, relative to V1. Approximately half of the surface area of V2 is dedicated to the representation of the central 5 degrees of the visual field. Calculations based on the CMF, receptive field scatter, and receptive field size revealed that the point-image size measured parallel to the V1/V2 border (2-3 mm) equals the width of a full cycle of cytochrome oxidase stripes in V2, suggesting a close correspondence between physiological and anatomical estimates of the dimensions of modular components in this area.

Animals↗
PubMed2000

Visual areas in lateral and ventral extrastriate cortices of the marmoset monkey.

The representation of the visual field in visual areas of the dorsolateral, lateral, and ventral cortices was studied by means of extracellular recordings and fluorescent tracer injections in anaesthetised marmoset monkeys. Two areas, forming mirror-symmetrical representations of the contralateral visual field, were found rostral to the second visual area (V2). These were termed the ventrolateral posterior (VLP) and the ventrolateral anterior (VLA) areas. In both areas, the representation of the lower quadrant is located dorsally, between the foveal representation of V2 and the middle temporal crescent (MTc), whereas the representation of the upper quadrant is located ventrally, in the supratentorial cortex. A representation of the vertical meridian forms the common border of areas VLP and VLA, whereas the horizontal meridian is represented both at the caudal border of area VLP (with V2) and at the rostral border of area VLA (with multiple extrastriate areas). The foveal representations of areas VLP and VLA are continuous with that of V2, being located at the lateral edge of the hemisphere. The topographic and laminar patterns of projections from dorsolateral and ventral cortices to the primary (V1) and dorsomedial (DM) visual areas both support the present definition of the borders of areas VLP and VLA. These results argue against a separation between dorsolateral and ventral extrastriate areas and provide clues for the likely homologies between extrastriate areas of different species.

Animals↗
PubMed2003

Relay of visual information to the lateral geniculate nucleus and the visual cortex in albino ferrets.

The abnormal organization of the central visual pathways in the albino ferret has been characterized anatomically and physiologically. Recordings in dorsal lateral geniculate nucleus of the albino ferret show that lamina A1, which receives an aberrant projection from the contralateral eye, contains an extensive representation of the ipsilateral visual hemifield with receptive fields located up to 35 degrees from the vertical meridian. This is not the case in pigmented ferrets, for which the vast majority of units, activated through either the contralateral or ipsilateral eye, have receptive fields confined to the contralateral hemifield. The few fields found in the ipsilateral hemifield are driven through the contralateral eye and none is more than 10 degrees from the midline. Cortical topography was studied by making closely spaced electrode penetrations across the area 17/18 border. In pigmented animals, the reversal of topography at the border is characterized by units with receptive fields centered a few degrees into the ipsilateral hemifield. In 22 of 25 albinos, the "Boston" aberrant topography was found: the representation of the vertical meridian is within area 17, rather than at the area 17/18 border. Instead, at the area 17/18 border, there is a reversal in the topographic progression at up to 30 degrees into the ipsilateral hemifield. This pattern was most pronounced in the upper visual field. In agreement with the "Boston" physiology, injections of retrograde tracer made in area 17 usually label neurons in either lamina A or the part of lamina A1 that is aberrantly innervated by the contralateral eye. A column of labeled cells extending through all geniculate layers is rarely seen in albinos, although this is commonly the pattern in pigmented ferrets.

Action Potentials↗
PubMed1979

Behavioral and electrophysiological effects of unilateral optic tract section in ordinary and Siamese cats.

In ordinary cats, section of one optic tract produced a complete contralateral hemianopsia in both eyes. Single-unit recordings showed a normal representation of the contralateral nasal retina and ipsilateral temporal retina in the SC on the side of the intact optic tract. In addition, in the rostral portion of this SC there was a representation of a small portion of the contralateral temporal retina. This portion was apposed to the vertical meridian and its width was at most 6 degrees. In the anterior half of the SC on the side of the optic tract section, despite the interruption of any direct optic input, there was an extensive representation of the ipsilateral nasal retina and the contralateral temporal retina. This indirect visual input to the SC ipsilateral to the optic tract section was absent in a cat with a section of the forebrain commissures. In Boston Siamese cats, section of one optic tract led to a virtually complete blindness in the eye contralateral to the section, whereas the other eye retained a full visual field, although the responsiveness of the temporal retina beyond 20 degrees from the vertical meridian was reduced. Similarly, the nasal hemiretina and most of the temporal hemiretina on the side of the section were represented in the opposite SC, whereas stimulation of the eye contralateral to the section could not drive SC units. There was some evidence that the visual field of the eye on the side of the section could at least in part be represented in the SC on the same side. The findings indicate that the crossed projections from temporal hemiretina in the ordinary cat, and the uncrossed projections from temporal hemiretina in the Siamese cat are insufficient by themselves to sustain visual orientation and to drive SC neurons. Each half of the visual field in the ordinary cat, and the field of each eye in the Siamese cat, can be represented in the ipsilateral SC via across-the-midline, indirect connections.

Animals↗
PubMed1981

Visual topography of V2 in the macaque.

The representation of the visual field in the area adjacent to striate cortex was mapped with multiunit electrodes in the macaque. The animals were immobilized and anesthetized and in each animal 30 to 40 electrode penetrations were typically made over several recording sessions. This area, V2, contains a topographically organized representation of the contralateral visual field up to an eccentricity of at least 80 degrees. The representation of the vertical meridian is adjacent to that in striate cortex (V1) and forms the posterior border of V2. The representation of the horizontal meridian in V2 forms the anterior border of V2 and is split so that the representation of the lower visual field is located dorsally and that of the upper field ventrally. As in V1, the representation of the central visual field is magnified relative to that of the periphery. The area of V2 is slightly smaller than that of V1. At a given eccentricity, receptive field size in V2 is larger than in V1. The myeloarchitecture of V2 is distinguishable from that of the surrounding cortex. The location of V2 corresponds, at least approximately, to that of cytoarchitectonic Area OB. V2 is bordered anteriorly by several other areas containing representations of the visual field.

Animals↗
PubMed1982

Exposure to lines of only one orientation modifies dendritic morphology of cells in the visual cortex of the cat.

To determine whether selective exposure to lines of one orientation modifies the shape of the dendritic fields of cells in visual cortex, we examined the dendritic morphology of neurons in area 17 of five normally reared cats, five cats reared viewing only vertical lines, and three cats reared viewing only horizontal lines. Kittens were placed with their mothers into a totally dark room before their eyes had opened. Beginning at 4 weeks of age, the kittens were brought out for daily periods of exposure wearing masks that limited the vision of each eye to a field of three vertical lines or three horizontal lines. After a minimum of 170 hours of exposure, the animals were killed and blocks of visual cortex were impregnated by the Golgi-Kopsch procedure and cut tangential to the pial surface. Complete neurons from layers III and IV were drawn with the aid of a camera lucida, and the orientations of the dendritic fields wer analyzed using Sholl diagrams. In normal cats, the distributions of the orientations of dendritic fields were uniform, whereas in strip-reared cats, the distributions for the layer III pyramidal cells were shifted. The direction of this shift varied with the experience of the cat: In cats reared viewing only vertical lines, the dendritic fields were oriented orthogonal to the representation of the vertical meridian, and in cats reared viewing only horizontal lines, the fields were oriented parallel to the representation of the vertical meridian. In contrast, the distribution of dentritic orientations for the stellate cells was not affected by stripe-rearing. These results demonstrate a morphological effect of early visual experience that is specific to the particular stimulus presented during rearing and suggest that (1) cortical cells differ in the degree to which they can be modified by such experience, and (2) the dendritic morphology of cortical neurons is related to their preferred orientations.

Animals↗
PubMed1983

Relationship between preferred orientation and receptive field position of neurons in cat striate cortex.

It has been known for two decades that neurons in mammalian visual cortex respond selectively to stimuli falling on the retina at a particular angular orientation (Hubel and Wiesel, '62). Recent evidence suggests that most cat retinal ganglion cells (Levick and Thibos, '82) and relay cells (Vidyasagar and Urbas, '82) in the cat's dorsal lateral geniculate nucleus are also orientation selective. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis, most retinal ganglion cells have oriented dendritic fields (Leventhal and Schall, '83) and respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick an Thibos, '82). This relationship is strongest close to the horizontal meridian (the visual streak) of the retina (Leventhal and Schall, '83). To determine if a relationship between preferred orientation and polar angle exists in visual cortex, the preferred orientations and receptive field positions of 768 striate cortical neurons were studied. As in the retina, a systematic relationship exists between preferred orientation and visual field position in area 17. In parts of striate cortex 15--80 degrees from the area centralis projection there is a strong tendency for cells to respond best to lines oriented radially. In regions 4--15 degrees from the area centralis projection this relationship appears weaker. In regions subserving the central 4 degrees of visual angle no such relationship exists. Throughout area 17 the relationship between preferred orientation and polar angle is strongest in regions subserving the horizontal meridian.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Termination patterns of individual X- and Y-cell axons in the visual cortex of the cat: projections to area 18, to the 17/18 border region, and to both areas 17 and 18.

Horseradish peroxidase was injected intracellularly into single, physiologically identified X- and Y-cell geniculocortical axons that projected to area 18, to the 17/18 border region, or to both areas 17 and 18 via branching axons. The axon terminal fields in cortex were labeled anterogradely, and the cell bodies of the axons in the A-laminae, lamina C, and the medial interlaminar nucleus (MIN) of the dorsal lateral geniculate nucleus (LGN) were labeled retrogradely. The laminar projections in area 18 of eight Y-cells and one geniculate, non-Y-cell were analyzed. Most of the cells arborized densely within layer IVa and the lower 200 to 400 microns of layer III. Most provided little or no input to layer IVb or layer VI. Thus, the laminar projections of Y-cells to layer IV of area 18 were similar to those of their area 17 counterparts, although the input to layer III was greater and rose much higher in area 18 than in area 17. The terminal arbors in area 18 were two to three times larger in lateral extent than those in area 17. They spread over 2.0 to 2.8 mm2 of layer IV and occupied proportionately much greater regions of area 18 than the Y-cell arbors in area 17. This may partially account for the large receptive fields of cortical cells in area 18, and it indicates that a small region of area 18 may receive converging inputs from a relatively wide retinotopic region of the LGN. The terminal arbors were also highly asymmetric, generally being two to four times longer anteroposteriorly than mediolaterally. These asymmetric arbors may form the structural basis for the anisotropic organization of the retinotopic map in area 18. We recovered three cells (two Y, one X) whose axons arborized in the border zone between areas 17 and 18. One Y-cell axon had a receptive field located in the ipsilateral visual hemifield and it arborized in a small region restricted almost exclusively to the border zone. The other two cells had receptive fields on or adjacent to the vertical meridian, and they terminated on either side of the 17/18 border region as well as within it. Thus, geniculate afferents representing the ipsilateral hemifield or the vertical meridian appear to have different patterns of termination on and adjacent to the 17/18 border zone. Also, some X-cell input may invade area 18 in the region immediately adjacent to the border zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Visual topography of V1 in the Cebus monkey.

The representation of the visual field in the striate cortex (V1) was mapped with multiunit electrodes in the Cebus monkey. Nine Cebus apella, anesthetized with N2O and immobilized with pancuromium bromide were studied in repeated recording sessions. In each hemisphere, V1 contains a continuous representation of the contralateral visual hemifield. The representation of the vertical meridian (VM) forms the external border of V1 except at the anteriormost portion of the calcarine fissure. The representation of the horizontal meridian (HM) divides the area so that the representation of the lower visual field is located dorsally, and that of the upper field ventrally. The convoluted surface of V1 can be only partially unfolded, and no precise "flattened" map can be obtained without introducing surface discontinuities. The visual topography of V1 is presented in a series of coronal sections and in "flattened" maps. The representation of the central visual field is magnified relative to that of the periphery in V1. The evaluation of the cortical magnification factors measured along isoeccentric and isopolar dimensions in the partially unfolded model of V1 revealed anisotropies in the representation of the visual field with larger magnification along isopolar lines than along isoeccentric lines. Receptive field size increases with increasing eccentricity, whereas point image size decreases with increasing eccentricity.

Animals↗
PubMed1988

Projections of the cochlear nuclei and nucleus laminaris to the inferior colliculus of the barn owl.

The barn owl determines the directions from which sounds emanate by computing the interaural differences in the timing and intensity of sounds. These cues for sound localization are processed in independent channels originating at nucleus magnocellularis (NM) and nucleus angularis (NA), the cochlear nuclei. The cells of NM are specialized for encoding the phase of sounds in the ipsilateral ear. The cells of NA are specialized for encoding the intensity of sounds in the ipsilateral ear. NM projects solely, bilaterally, and tonotopically to nucleus laminaris (NL). NL and NA project to largely nonoverlapping zones in the central nucleus of the inferior colliculus (ICc), thus forming hodological subdivisions in which time and intensity information may be processed. The terminal field of NL occupies a discrete zone in the rostromedial portion of the contralateral ICc, which we have termed the "core" of ICc. The terminal field of NA surrounds the core of ICc and thus forms a "shell" around it. The projection from NL to the core conserves tonotopy. Low-frequency regions of NL project to the dorsal portions of the core whereas higher-frequency regions project to more ventral portions. This innervation pattern is consistent with earlier physiological studies of tonotopy. Physiological studies have also suggested that NL and the core of ICs contain a representation of the location of a sound source along the horizontal axis. Our data suggest that the projection from NL to the core preserves spatiotopy. Thus, the dorsal portion of NL on the left, which contains a representation of eccentric loci in the right hemifield, innervates the area of the right ICc core that represents eccentric right loci. The more ventral portion of the left NL, which represents loci close to the vertical meridian, innervates the more rostral portions of the right core, which also represents loci near the vertical meridian.

Afferent Pathways↗
PubMed1988

Representation of the visual field in the second visual area in the Cebus monkey.

The representation of the visual field in the second visual area (V2) was reconstructed from multiunit visual responses and anatomical tracers. Receptive field plotting was performed during multiple recording sessions in seven Cebus apella monkeys under N2O/O2 and immobilized with pancuronium bromide. V2 forms a continuous belt of variable width around striate cortex (V1) except at the most anterior portion of the calcarine sulcus. In each hemisphere V2 contains a visuotopic representation of the contralateral visual hemifield. The representation of the vertical meridian is adjacent to that of V1 and forms the posterior border of V2. The representation of the fovea of V2 is adjacent to that of V1. The representation of the horizontal meridian (HM) is continuous with that of V1; then it splits to form the anterior border of V2, both dorsally and ventrally. The lower quadrant of the visual field is represented dorsally and the upper quadrant ventrally. The visual topography of V2 is coarser than that of V1. In V2, receptive fields corresponding to recording sites separated by a cortical distance of up to 4 mm may represent the same portion of the visual field. In three additional animals, combined injections of fluorescent tracers along the HM representation in V1 yielded two projection sites at the anterior border of V2. The split of the HM representation is estimated to occur at an eccentricity below 1 degree. Quantitative analysis showed that in V2 the representation of the central visual field is magnified relative to that of the periphery. The cortical magnification factor is greater along the isopolar dimension than along the isoeccentric one. Receptive field size in V2 increases with increasing eccentricity. In sections stained for myelin by the Heidenhein-Wöelcke method V2 can be distinguished from the surrounding cortex for most of its extent.

Animals↗
PubMed1989

Visual area MT in the Cebus monkey: location, visuotopic organization, and variability.

The representation of the visual field in the dorsal portion of the superior temporal sulcus (ST) was studied by multiunit recordings in eight Cebus apella, anesthetized with N2O and immobilized with pancuronium bromide, in repeated recording sessions. On the basis of visuotopic organization, myeloarchitecture, and receptive field size, area MT was distinguished from its neighboring areas. MT is an oval area of about 70 mm2 located mainly in the posterior bank of the superior temporal sulcus. It contains a visuotopically organized representation of at least the binocular visual field. The representation of the vertical meridian forms the dorsolateral, lateral, and ventrolateral borders of MT and that of the horizontal meridian runs across the posterior bank of ST. The fovea is represented at the lateralmost portion of MT, while the retinal periphery is represented medially. The representation of the central visual field is magnified relative to that of the periphery in MT. The cortical magnification factor in MT decreases with increasing eccentricity following a negative power function. Receptive field size increases with increasing eccentricity. A method to evaluate the scatter of receptive field position in multiunit recordings based on the inverse of the magnification factor is described. In MT, multiunit receptive field scatter increases with increasing eccentricity. As shown by the Heidenhain-Woelcke method, MT is coextensive with two myeloarchitectonically distinct zones: one heavily myelinated, located in the posterior bank of ST, and another, less myelinated, located at the junction of the posterior bank with the anterior bank of ST. At least three additional visual zones surround MT: DZ, MST, and FST. The areas of the dorsal portion of the superior temporal sulcus in the diurnal New World monkey Cebus are comparable to those described for the diurnal Old World monkey, Macaca. This observation suggests that these areas are ancestral characters of the simian lineage and that the differences observed in the owl monkey may be secondary adaptations to a nocturnal ecological niche.

Animals↗