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PubMed1978

Lateral asymmetries in visual perception with and without eye movements.

A signal detection analysis was made of single letter recognition in the right and left visual fields. When letters were presented 2 degrees 3' to the right or left of a central fixation there were no significant differences between the fields in perceptual accuracy independent of bias when the subject maintained a central fixation point. However, when subjects were free to move their eyes a right field advantage was found. The results were discussed in terms of attentional bias theories and hemispheric specialization theories.

Cerebral Cortex↗
PubMedDate not supplied

[Ontogenetic characteristics of the development of slow negative and positive potentials during the performance of a visual perceptive task].

In age aspect, topography and parameters were studied of late EPs and slow negative components (CNV) to successively presented visual stimuli: the preliminary signal and two compared contour images. Age characteristics of development of the frontal negativity N450 and the late positive complex (LPC) were revealed. in children 7 and 10 years old, the component N450 was present in response both to the preliminary and the first stimulus in the compared pair; LPC was recorded to all three presented visual stimuli. In 17 years old subjects and in adults, selectivity of N450 formation in the EP to the first of the compared stimuli and LPC to the second (imperative) stimulus correlates with involvement of rostral brain areas--central in youths, central and frontal ones in adults--both in the process of waiting (CNV) and evaluation of coming information (LPC).

Adolescent↗
PubMed1996

Plasticity in visual perception and physiology.

Many factors influence our perception of local features. What we see is not strictly a reflection of the physical characteristics of a scene, but instead is highly dependent on the processes by which our brain attempts to interpret the scene. As a result, our percepts are shaped by the context within which local features are presented, by our previous visual experiences (operating over a wide range of time scales), and by our expectations of what is likely to be before us. The substrate for these influences is found in the lateral interactions operating within individual areas of the cerebral cortex and in the feedback from higher to lower order cortical areas.

Animals↗
PubMed1997

Functional segregation and temporal hierarchy of the visual perceptive systems.

In extending our previous work, we addressed the question of whether different visual attributes are perceived separately when they belong to different objects, rather than the same one. Using our earlier psychophysical method, but separating the attributes to be paired in two different halves of the screen, we found that human subjects misbind the colour and the direction of motion, or the colour and the orientation of lines, because colour, form, and motion are perceived separately and at different times. The results therefore show that there is a perceptual temporal hierarchy in vision.

Color Perception↗
PubMed1996

Visual perceptions of head-fixed and trunk-fixed anterior/posterior axes.

The purpose of the present experiment was to determine the preferred visual "straight ahead" or anterior/posterior (a/p) axis at the perceptual level. The ability of 12 neurologically normal, young adult subjects to position a rod parallel to the head and trunk a/p axes while viewing eccentrically located visual targets were studied under six conditions: 1. fixed-subjects stood erect with the head aligned to the trunk and viewed a central target while visually aligning a hand-held rod to the head and trunk a/p axis. 2. eyes-subjects moved only their eyes to view eccentric targets and aligned the rod to the head and trunk a/p axis. 3. head-trunk-subjects viewed the eccentric targets by rotating the head about a vertical axis and aligned the rod to the trunk a/p axis. 4. head-head-subjects viewed the targets as in 3 and positioned the rod parallel to the head a/p axis. 5. trunk-head-subjects viewed the targets by rotating the trunk and head as a unit about the vertical axis and aligned the rod parallel to the head a/p axis (note that the head and trunk a/p axes were misaligned by the experimenter prior to target viewing). 6. trunk-trunk-subjects viewed targets as in 5 and positioned the rod parallel to the trunk a/p axis. Subjects performed 25-35 consecutive trials within each condition. Perceptual errors were similar for aligning the rod to the trunk and head a/p axes; however, moving the trunk produced much larger constant and variable perceptual errors than moving the head. In a second experiment, four subjects controlled the position of a lighted rod held by a robot arm in complete darkness. They were instructed to align the rod to either the head or trunk a/p axis under conditions similar to the fixed, head-trunk, and head-head tasks described above. Perceptual errors were much larger when aligning the rod to the head a/p axis than to trunk a/p axis when the head was moved. This shows that the trunk a/p axis is clearly preferred at the perceptual level when visual background cues are not present. These data strongly suggest that the visual coordinate system uses a trunk-fixed a/p axis to define the subjective straight-ahead direction and right/left position of a target. Implications of these findings for sensorimotor transformations in control of upper limb movements to visual targets are discussed.

Adult↗
PubMed1983

Visual perception fields in the superficial layers of the opossum's superior colliculus: representation of the ipsi and contralateral hemifields by each eye.

Visual receptive fields of single units in the superior colliculus of the opossums were analysed in regions representing the ipsilateral (rostral pole - RP) and the contralateral hemifields (direct binocular region - DBR) close to and including the representation of the horizontal meridian. Of 242 units half had receptive field centres of the contralateral eye at the ipsilateral hemifield and the other half at the contralateral hemifield. The proportion of units driven by the ipsilateral eye was considerably smaller at the RP than at the DBR and the frequency of unit response to this eye diminished within the ipsilateral hemifield with progressively more rostral penetrations in the RP. The midline was unequally represented by the two eyes in RP units: while 24 out of 26 receptive fields of the ipsilateral eye straddled the vertical meridian, only 50 out of 120 of the contralateral eye did so. Furthermore, at the RP receptive fields of units responsive to the contralateral eye extended up to 46.8 degrees into the ipsilateral visual field while those mapped for the ipsilateral eye extended only up to 26 degrees. As a result of this tendency for the receptive fields of the ipsilateral, but not the contralateral eye, to overlap the vertical meridian, progressively more rostral recordings yielded an increase in the binocular convergent disparity as a function of the eccentricity for the receptive field of the contralateral eye. Since the disparity didn't vary with the eccentricity in the DBR units, we suggest that stimuli at the midline and close to the animal might be the natural ones to drive large disparity units present in the RP.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗