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.     

Location constancy and its effect on visual selection.

The present study investigated how location constancy influences selective attention to a cued location. The relative effectiveness of target/distractor distance and target/distractor compatibility were studied under covert and overt attention conditions. Experiment 1 measured reaction time and error rates to a scaled target letter that appeared at varied locations from 0.62 to 20 deg. Experiments 2 and 3 looked at covert/overt attention when the target location was fixed rather than varied within a block of trials. To provide a comprehensive assessment of the two primary variables across location constancy conditions, effect sizes for these results as well as for related past research (Goolkasian, 1999; Goolkasian and Tarantino, 1999) are presented. The findings suggest that the location of the target (foveal vs peripheral) does not influence attentional patterns as much as the consistency of its location. When a target appears at varied locations from trial to trial, distractor compatibility effects are in general stronger than the effect of target/distractor distance. However, the relative importance of these two variables reverses when the presentation location of the target is fixed at a constant location.     

Temporal hierarchy of the visual perceptive systems in the Mondrian world.

Our earlier psychophysical work has shown that colour and motion are not perceived at the same time, with colour leading motion by about 50-100 ms. In pursuing this work, we thought it would be interesting to use a more complex colour stimulus, one in which the wavelength composition of the light reflected or emitted from surfaces changes continually, without entailing a change in the perceived colour (colour constancy). We therefore used a Mondrian figure--an abstract multi-coloured scene with no recognizable objects--against which squares (either red or green) moved up and down, changing colour from red to green in various phase differences with the change in direction of motion. The red and green squares changed continually in their spectral characteristics, as did every other patch on the Mondrian. The results showed that colour is still perceived before motion, by about 80 ms.     

Recovery from monocular deprivation in the monkey. I. Reversal of physiological effects in the visual cortex

This is a study of the effects of monocular deprivation, reverse suturing (opening the deprived eye with closure of the other) and reopening of the deprived eye alone (without closing the other) on the physiological organization of the primary visual cortex in monkeys (Erythrocebus patas). All animals were initially monocularly deprived by suture of the lids of the right eye from soon after birth until about 4 weeks of age (24-29 days). In a monocularly deprived animal, recordings were taken from area 17 at 24 days. Already most neurons recorded outside layer IVc, were strongly or completely dominated by functional input from the left eye. The Non-oriented cells of layer IVc, where the bulk of the afferent input terminates, were also mainly dominated by the left eye. Although segregation of input from the two eyes was not complete, large areas of layer IVc were already monocularly dominated by the left eye. Four animals were reverse-sutured at about 4 weeks and recorded 3, 6, 15 and 126 days later. In each animal the pattern of ocular dominance was fairly similar within and outside layer IVc. Even with only 3 days of forced usage of the initially deprived right eye, about half of all cells recorded had become dominated by it, and the process of "recapture' of cortical cells by the initially deprived eye was apparently complete within 15 days. In layer IVc, the recovery took the form of an expansion of zones dominated by the deprived eye, as if the originally shrunken stripes of afferent termination had become enlarged. Binocularly driven neurons were rare at all stages, in all layers, but when present and orientation-selective, they had similar preferred orientations in the two eyes. Likewise the "columnar' sequences of preferred orientation continued without obvious disruption on shifting from regions dominated by one eye to those dominated by the other. Simply reopening the deprived eye at about 4 weeks, for 15 to 96 days caused no detectable change in the overall ocular dominance of cortical cells and, on average, no expansion of right-eye dominance columns in layer IVc. Therefore the recovery seen after reverse suturing depends not just on the restoration of normal activity to axons carrying information from the right eye, but on the establishment of a competitive advantage, through the right eye being made more active than the left.     

Objective criteria for acceptability and constancy tests of digital subtraction angiography

PurposeDemonstrate an objective procedure to quantify image quality in digital subtraction angiography (DSA) and suggest thresholds for acceptability and constancy tests.MethodsSeries of images were obtained in a DSA system simulating a small (paediatric) and a large patient using the dynamic phantom described in the IEC and DIN standards for acceptance tests of DSA equipment. Image quality was quantified using measurements of contrast-to-noise ratio (CNR). Overall scores combining the CNR of 10–100 mg/ml Iodine at a vascular diameter of 1–4 mm in a homogeneous background were defined. Phantom entrance surface air kerma (K_a,e) was measured with an ionisation chamber.ResultsThe visibility of a low-contrast vessel in DSA images has been identified with a CNR value of 0.50 ± 0.03. Despite using 14 times more K_a,e (8.85 vs 0.63 mGy/image), the protocol for large patients showed a decrease in the overall score CNR_sum of 67% (4.21 ± 0.06 vs 2.10 ± 0.05). The uncertainty in the results of the objective method was below 5%.ConclusionObjective evaluation of DSA images using CNR is feasible with dedicated phantom measurements. An objective methodology has been suggested for acceptance tests compliant with the IEC/DIN standards. The defined overall scores can serve to fix a reproducible baseline for constancy tests, as well as to study the device stability within one acquisition series and compare different imaging protocols. This work provides aspects that have not been included in the recent European guidelines on Criteria for Acceptability of Medical Radiological Equipment.     

Cardiopulmonary regulation after rapid-eye-movement sleep deprivation.

Arterial blood pressure, chest movement, electroencephalogram, and electromyogram were monitored in six normotensive Sprague-Dawley rats for 4 h/day 3 days before and 4 days after 114 h of rapid-eye-movement (REM) sleep deprivation. During recovery sleep immediately after REM sleep deprivation (RD), there was a significant increase in the amount of time spent in REM sleep. During this rebound in REM sleep, there was a significant rise (26%) in heart rate in wakefulness, non-REM sleep, and REM sleep during the first 4 h after RD. Systolic blood pressure was also significantly elevated (14%) but only during wakefulness before recovery sleep. Rats with the greatest waking systolic blood pressure after RD had the lowest REM sleep rebound in the 4 h immediately after RD (r = -0.885, P less than 0.05). The rise in heart rate, systolic blood pressure, and REM sleep time evident on day 1 immediately after RD was absent on recovery days 2-4. The respiratory rate tended to be higher throughout the recovery period in every state of consciousness; however, these values never reached the level of significance. In the initial recovery sleep period, regulation of heart rate was more disrupted by REM sleep deprivation than either arterial blood pressure or respiratory rate.     

Work of the human visual system. I. Adequate visual stimulus]

It is shown that the adequate stimulus permitting to detect the presence of colour differentiation in the visual field is the change of relative space-time differences of light actions in different retinal points. Differences only in space or only in time are not sufficient for perception.     

Development of GABAA receptors in the central visual structures of rat brain. Effect of visual pattern deprivation

The postnatal development of high-affinity 3H-muscimol binding to GABAA receptors was studied in the lateral geniculate nucleus, superior colliculus, frontal and visual cortex of the rat brain. In the lateral geniculate nucleus 3H-muscimol binding rises from day 10 through day 37 reaching the highest value during the entire development followed by a slight decrease until adulthood. In the superior colliculus 3H-muscimol binding increased continuously from day 10 through day 37, and then decreased until day 50 reaching the adult value. In the visual and frontal cortex, binding reached the highest levels on days 14 and 25, respectively, persisted until day 37 followed by a slight decrease until adulthood. The ontogeny of 3H-muscimol binding sites in the visual regions does not essentially differ from that in other brain regions, suggesting that the appearance of 3H-muscimol binding sites in the visual system is not correlated with the functional maturation of the visual system. Unilateral eyelid closure from day 11 until day 25 did not affect the development of GABAA receptors in any of the central visual regions examined, indicating the lack of environmentally controlled mechanism.     

Neural mechanisms of recovery following early visual deprivation

Natural patterned early visual input is essential for the normal development of the central visual pathways and the visual capacities they sustain. Without visual input, the functional development of the visual system stalls not far from the state at birth, and if input is distorted or biased the visual system develops in an abnormal fashion resulting in specific visual deficits. Monocular deprivation, an extreme form of biased exposure, results in large anatomical and physiological changes in terms of territory innervated by the two eyes in primary visual cortex (V1) and to a loss of vision in the deprived eye reminiscent of that in human deprivation amblyopia. We review work that points to a special role for binocular visual input in the development of V1 and vision. Our unique approach has been to provide animals with mixed visual input each day, which consists of episodes of normal and biased (monocular) exposures. Short periods of concordant binocular input, if continuous, can offset much longer episodes of monocular deprivation to allow normal development of V1 and prevent amblyopia. Studies of animal models of patching therapy for amblyopia reveal that the benefits are both heightened and prolonged by daily episodes of binocular exposure.