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PubMed1997

Uncertain responses by humans and rhesus monkeys (Macaca mulatta) in a psychophysical same-different task.

The authors asked whether animals, like humans, use an uncertain response adaptively to escape indeterminate stimulus relations. Humans and monkeys were placed in a same-different task, known to be challenging for animals. Its difficulty was increased further by reducing the size of the stimulus differences, thereby making many same and different trials difficult to tell apart. Monkeys do escape selectively from these threshold trials, even while coping with 7 absolute stimulus levels concurrently. Monkeys even adjust their response strategies on short time scales according to the local task conditions. Signal-detection and optimality analyses confirm the similarity of humans' and animals' performances. Whereas associative interpretations account poorly for these results, an intuitive uncertainty construct does so easily. The authors discuss the cognitive processes that allow uncertainty's adaptive use and recommend further comparative studies of metacognition.

Adult↗
PubMed1996

Contrast and illumination effects on explicit and implicit measures of memory.

The present study examined the effect of changing the contrast polarity and illumination of objects on explicit (episodic recognition) and implicit (fragment naming or object-nonobject decision) memory tasks. Changes in contrast polarity of line drawings of objects did not affect priming on fragment naming or on object-nonobject decision tasks but adversely affected recognition judgments. Similarly, changes in illumination did not affect priming on the object-nonobject decision task but adversely affected recognition memory. Together, the results suggest that implicit measures tap abstract descriptions of object structure useful for the purposes of object identification, whereas recognition memory taps descriptions that integrate shape information with lower level perceptual information. It is argued that lower level perceptual information influences episodic recognition because it provides a cue to the spatiotemporal context within which the prior encounter with the object occurred.

Adult↗
PubMed2004

Perceiving the intensity of light.

The relationship between luminance (i.e., the photometric intensity of light) and its perception (i.e., sensations of lightness or brightness) has long been a puzzle. In addition to the mystery of why these perceptual qualities do not scale with luminance in any simple way, "illusions" such as simultaneous brightness contrast, Mach bands, Craik-O'Brien-Cornsweet edge effects, and the Chubb-Sperling-Solomon illusion have all generated much interest but no generally accepted explanation. The authors review evidence that the full range of this perceptual phenomenology can be rationalized in terms of an empirical theory of vision. The implication of these observations is that perceptions of lightness and brightness are generated according to the probability distributions of the possible sources of luminance values in stimuli that are inevitably ambiguous.

Attention↗
PubMed1992

Inverse duration effects in partial report.

In partial-report experiments, an array of stimuli is displayed briefly, followed by a probe indicating the items to be reported. When exposure duration of the array is increased, 2 contrasting outcomes have been found: Some experiments find that performance improves (direct-duration effect); others find that it deteriorates (inverse-duration effect). The objective here was to identify the reasons for the discrepant results. This was done by investigating the roles played by 5 factors that differed between the 2 sets of contrasting studies. An inverse-duration effect was obtained in each of 6 experiments; its magnitude was affected by retinal eccentricity and by the number of items denoted by the probe. The effect was independent of array configuration and of number of items in the array. The direct-duration effect was shown to arise from a confounding of exposure duration and brightness.

Adult↗
PubMed2004

Face recognition is affected by similarity in spatial frequency range to a greater degree than within-category object recognition.

Previous studies have suggested that face identification is more sensitive to variations in spatial frequency content than object recognition, but none have compared how sensitive the 2 processes are to variations in spatial frequency overlap (SFO). The authors tested face and object matching accuracy under varying SFO conditions. Their results showed that object recognition was more robust to SFO variations than face recognition and that the vulnerability of faces was not due to reliance on configural processing. They suggest that variations in sensitivity to SFO help explain the vulnerability of face recognition to changes in image format and the lack of a middle-frequency advantage in object recognition.

Adolescent↗
PubMed2006

When is search for a static target among dynamic distractors efficient?

Intuitively, dynamic visual stimuli, such as moving objects or flashing lights, attract attention. Visual search tasks have revealed that dynamic targets among static distractors can indeed efficiently guide attention. The present study shows that the reverse case, a static target among dynamic distractors, allows for relatively efficient selection in certain but not all cases. A static target was relatively efficiently found among distractors that featured apparent motion, corroborating earlier findings. The important new finding was that static targets were equally easily found among distractors that blinked on and off continuously, even when each individual item blinked at a random rate. However, search for a static target was less efficient when distractors abruptly varied in luminance but did not completely disappear. The authors suggest that the division into the parvocellular pathway dealing with static visual information, on the one hand, and the magnocellular pathway common to motion and new object onset detection, on the other hand, allows for efficient filtering of dynamic and static information.

Adult↗
PubMed2006

Faces are "spatial"--holistic face perception is supported by low spatial frequencies.

Faces are perceived holistically, a phenomenon best illustrated when the processing of a face feature is affected by the other features. Here, the authors tested the hypothesis that the holistic perception of a face mainly relies on its low spatial frequencies. Holistic face perception was tested in two classical paradigms: the whole-part advantage (Experiment 1) and the composite face effect (Experiments 2-4). Holistic effects were equally large or larger for low-pass filtered faces as compared to full-spectrum faces and significantly larger than for high-pass filtered faces. The disproportionate composite effect found for low-pass filtered faces was not observed when holistic perception was disrupted by inversion (Experiment 3). Experiment 4 showed that the composite face effect was enhanced only for low spatial frequencies, but not for intermediate spatial frequencies known be critical for face recognition. These findings indicate that holistic face perception is largely supported by low spatial frequencies. They also suggest that holistic processing precedes the analysis of local features during face perception.

Adolescent↗
PubMed2004

Vernier threshold in patients with schizophrenia and in their unaffected siblings.

The aim of this study was to investigate magnocellular (M) and parvocellular (P) visual functions in nonmedicated patients with schizophrenia and in their unaffected siblings. Possible abnormalities in cortical integration of retinal receptive fields also were addressed. Twenty-two nonmedicated patients with schizophrenia, their unaffected siblings, and 20 age- and IQ-matched healthy control subjects received 4 vernier acuity tasks (blue-on-yellow, frequency-doubling, achromatic low and high contrast conditions) in which they were asked to detect the spatial alignment of dots and gratings. Results revealed that the patients with schizophrenia and their unaffected siblings showed selective dysfunctions in the frequency-doubling and achromatic low contrast conditions, which were devoted to investigate M pathways. In the isoluminant blue-on-yellow and high contrast achromatic conditions, there were no significant differences between the experimental groups. These results suggest that the deficit of M pathway is an endophenotype of schizophrenia.

Adult↗
PubMed2006

Spatial relational learning persists following neonatal hippocampal lesions in macaque monkeys.

The hippocampus is important for the acquisition of spatial representations of the environment and consequently in contextual memory. This suggests that the neural substrates underlying spatial cognition might be essential for remembering specific life episodes. Indeed, hippocampal lesions prevent spatial relational learning in adult rodents and monkeys, and result in profound amnesia in adult humans. In contrast, we show here that monkeys with neonatal hippocampal lesions learned new spatial relational information. Our experiments suggest that early hippocampal damage leads to functional brain reorganization that enables spatial information to be acquired through the use of brain regions that normally do not subserve this function.

Adaptation, Physiological↗
PubMed2003

Cerebral regions processing first- and higher-order motion in an opposed-direction discrimination task.

Using PET, we studied the processing of different types of motion in an opposed-direction discrimination task. We used first-order motion and two types of higher-order motion (presented as moving gratings with stripes defined by flickering texture and kinetic boundaries, respectively). In these experiments, we found that all types of motion activate a common set of cortical regions when comparing a direction discrimination task to a detection of the dimming of the fixation point. This set includes left hV3A, bilateral hMT/V5+ and regions in the middle occipital gyrus, bilateral activations in the posterior and anterior parts of the intraparietal sulcus, bilateral precentral gyrus, medial frontal cortex and regions in the cerebellum. No significant differences were observed between different types of motion, even at low statistical thresholds. From this we conclude that, under our experimental conditions, the same cerebral regions are involved in the processing of first-order and higher-order motion in an opposed-direction discrimination task.

Acoustic Stimulation↗
PubMed2001

Learning in the field: curriculum issues in a diploma in public health nursing.

Illuminative evaluation of a public health nursing curriculum shows that there was a gap between theory and practice, originating in the ways in which public health nursing was understood in the field, and therefore during students' placements, and in the university. The difference was chiefly in how the community staff and the lecturers understood primary health care. The former had a 'medical/professional' understanding of primary health care, implying that the professional knows best and that the client is an individual, a family or a group. The lecturers held a philosophy of primary health care with special emphasis on partnership with clients at all levels: individual, family, group and community; the partnership approach was intended to permeate the entire curriculum. Besides philosophical differences, there were other features of the theory practice gap demonstrated elsewhere. Fieldwork practice is integral to learning public health nursing so these contrasts created a serious disjunction within the curriculum. Actual and potential ways of improving curriculum integration are discussed.

Community Health Nursing↗
PubMed1999

[Contrast enhancement in the public environment--improvement in orienting capacity of visually handicapped patients].

BACKGROUND: Partially sighted often experience problems in orientation in public areas. Individual visual aids can only be used with limitations. Improving light intensity and colour contrasts of timetables, information signs, direction symbols, etc. can provide remedies. Experimentally substantiated directives do not yet exist. PATIENTS AND METHODS: Experiments were conducted in 231 partially sighted subjects (binocular vision < 0.3) diagnosed as experiencing dullness when watching the media, having maculopathies, glaucomas, or dystrophic alterations of the retina or choroid, and in 43 normal subjects to determine the subjective assessment of colour and light-intensity contrasts. The presented contrast patterns were Hartmann-characters as infield (3.3 degrees) with a rectangular surround (19.5 degrees x 14.3 degrees). Three experimental series were carried out in which subjects assigned 14 non-coloured/non-coloured contrasts, 35 non-coloured/colour contrasts and 30 colour/colour contrasts to any of the five assessment classes of extremely poor, poor, optimal, sharp, extremely sharp. The colour contrasts consisted of combinations of yellow, green, red, purple, blue, and non-coloured. RESULTS: For non-coloured/non-coloured, the subjects preferred positive contrasts (bright infield, dark surround). Preferred contrast levels were 0.91 to 0.99 for positive contrasts and -0.96 to -0.99 for negative contrasts. For colour/non-coloured contrasts, 90% of the partially sighted preferred yellow as the foreground colour with a contrast level above 0.89. For colour/colour contrasts, optimal assessments of 90% of all partially sighted were yellow/purple and yellow/blue with contrast levels above 0.90. The determined results are applicable for the exact experimental contrast settings only. A field manual was prepared for planning and design of contrasts suited for the partially sighted in public areas. CONCLUSIONS: Partially sighted, in subjective contrasts assessment, prefer bright characters of signs on a dark background for both non-coloured and colour contrasts with contrast levels above 0.9. Yellow was the preferred infield colour.

Adolescent↗
PubMed1992

Cooperative representation of visual borders.

Recently it has been reported that the visual cortical cells which are engaged in cooperative coding of global stimulus features, display synchrony in their firing rates when both are stimulated. Alternative models identify global stimulus features with the course spatial scales of the image. Versions of the Munsterberg or Café Wall illusions which differ in their low spatial frequency content were used to show that in all cases it was the high spatial frequencies in the image which determined the strength and direction of these illusions. Since cells responsive to high spatial frequencies have small receptive fields, cooperative coding must be involved in the representation of long borders in the image.

Attention↗
PubMed1992

The reversed Müller-Lyer illusion and figure-ground organization theory.

When the shaft is shortened and reaches neither of the vertices of the two pairs of wings, a reversed Müller-Lyer illusion is observed: a shaft between inward-pointing wings appears to be longer than a shaft between the outward-pointing wings. In this paper it is examined whether this illusion can be explained in terms of figure-ground organization. A circle was used as the focal area, instead of a shaft or a pair of dots, so that the figure-ground character could be seen more definitely in this focal area. The apparent size of the focal circle was measured under different conditions with three variables (enclosure, wings direction, and depth). The focal circle appeared to be largest in the condition where the circle should appear most readily as a hole, ie in the single, wings-in, space condition. The circle appeared to be smallest in the condition where the circle should appear most readily as a disc, ie in the separate, wings-out, object condition. This is consistent with an explanation of the usual, as well as the reversed, Müller-Lyer illusion in terms of figure-ground organization theory.

Adult↗
PubMed1992

Amodal completion versus induced inhomogeneities in the organization of illusory figures.

An analysis is presented of a phenomenological model of illusory contours. The model is based on amodal completion as the primary factor giving rise to the illusory figure. In the experiment, conducted by the method of paired comparisons, the same parameter was manipulated in two series of equivalent configurations. The first series yielded examples of amodal completion, the second examples of illusory figures. Three groups of subjects evaluated the magnitude of completion, the brightness contrast of the illusory figure, and the contour clarity of the illusory figure. A control experiment was conducted, which demonstrated that in these configurations amodal completion and amodal continuation behave in the same way. Line displacement did not influence the brightness or the contour clarity of the illusory figures, though it influenced the magnitude of amodal completion. These results are in agreement with the energetic model developed by Sambin.

Adult↗
PubMed1992

Changes in infants' ability to switch visual attention in the first three months of life.

The abilities of 1-month-old and 3-month-old infants to shift their gaze from a central target to a peripheral target were compared in four experiments. In experiment 1 targets matched in mean luminance to the background were presented to infants in the periphery at varying levels of contrast. The contrast thresholds for target detection were found to be significantly different for 1-month-olds compared with 3-month-olds. With targets set close to these contrast thresholds, correct refixations and the latency for shifting attention were examined in experiment 2. Two conditions were used: a peripheral target was presented against a homogeneous background (noncompetition); and in the second condition, the patterned target appeared at one of two lighter peripheral windows set against a darker background (competition). Although there was no difference between the two age groups in the latency for shifting visual attention, 1-month-olds were found to make more directional errors in the competition condition. The competition effect of two potential targets on latencies was examined in experiment 3. In the competition condition, two identical peripheral patterned targets were presented to the infants. The 3-month-olds refixated more quickly to one of the double targets in the competition condition than to a single peripheral target, whereas 1-month-olds were slowed down by a double target display. Finally, in experiment 4 the ability of the infants to process and disengage from a central stimulus and to refixate towards a similar peripheral target was examined. This type of competition disrupted both the direction of the first eye movement and the latency to shift attention in both age groups. However, the effect was significantly greater for the 1-month-olds. Taken together, the results of these experiments demonstrate the greater disruption of fixation-shift behaviour in 1-month-olds compared with 3-month-olds when competing visual stimuli are used. This developmental change is explained in terms of maturation of executive cortical orienting systems over the first months of life.

Age Factors↗
PubMed1993

Discrimination of the shape of the masked inducing figure precedes perception of the illusory triangle.

Using the Kanizsa triangle in a free-inspection paradigm, Gellatly has shown that subjects report seeing an illusory triangle while apparently not phenomenally aware of the inducing areas. It is argued that Gellatly's procedure may induce response processes which camouflage early sensory processes. By forcing subjects to choose between two response alternatives, it was shown that when they could just perceive the illusory triangle, they could also correctly discriminate the shape of the inducing elements. Under the free-inspection procedure, the duration threshold for seeing the illusory triangle was about 9 ms while the threshold for discriminating the shape of the inducing elements was about 2 ms. A static representation of the dynamic procedure used by Gellatly has been derived, which shows a novel effect of contour completion across boundaries resulting in a ghostly white triangle.

Adult↗