Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “SIZE PERCEPTION”

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 1,621 records · Page 90Linked to original sources
PubMed2002

Functional coupling between the limbs during bimanual reach-to-grasp movements.

While it is frequently advantageous to be able to use our hands independently, many actions demand that we use our hands co-operatively. In this paper we present two experiments that examine functional binding between the limbs during the execution of bimanual reach-to-grasp movements. The first experiment examines the effect of gaze direction on unimanual and bimanual reaches. Even when subjects' eye movements are restricted during bimanual reaches so that they may only foveate one target object, the limbs remain tightly synchronized to a common movement duration. In contrast, grip aperture is independently scaled to the size of the target for each hand. The second experiment demonstrates however, that the independent scaling of grip aperture is task dependent. If the two target objects are unified so that they appear to be part of a single object, grip apertures become more similar across the hands (i.e., grip aperture to the large target object is reduced in size while peak aperture to the small target item is increased in size). These results suggest that the coupling of the limbs can operate at a functional level.

Adolescent↗
PubMed2000

Changes in the vertical size of a three-dimensional object drawn in weightlessness by astronauts.

The purpose of this study was to investigate the effects of weightlessness on mental representation of spatial cues. Two astronauts drew two groups of three-dimensional cubes with their eyes closed, one on Earth (preflight) and the other under weightless conditions during a 7-day orbital flight (inflight). Differences in the average height of the two groups of cubes were observed. The ratio of average length of the horizontal vs. the vertical lines of the inflight cubes increased significantly compared to that of the preflight cubes. The disappearance of the gravitational reference system, which determines on Earth the vertical direction, seems to influence the internal representation of the vertical dimension, (i. e. the height) of a three-dimensional object.

Analysis of Variance↗
PubMedDate not supplied

The Alderson-McGall hand function questionnaire for patients with Carpal Tunnel syndrome: a pilot evaluation of a future outcome measure.

The Alderson-McGall hand function questionnaire (AMHFQ) was developed to evaluate outcomes for patients with carpal tunnel syndrome (CTS). This pilot evaluation of 17 subjects with CTS involved the same battery completed twice prior to CTS release. The complete battery included evaluation of grip and pinch strength, static and dynamic two-point discrimination, dexterity using the Valpar Worksample for upper extremity range of motion, pain and hand function using visual analog scales (VASs), and the AMHFQ. The results indicated high internal consistency, with a Cronbach alpha value of 0.97. Intraclass correlation showed test-retest reliability in the 95th percentile for all items except one. Validity was demonstrated by AMHFQ correlations with all other battery items in the correct direction and significant correlations with dynamic two-point discrimination (r = -0.32), functional VAS (r = 0.3688), pain VAS (r = 0.36), and grip strength (r = 0.3867). These results suggest that the AMHFQ has clinical utility for patients with CTS. Further research to confirm these findings and determine sensitivity to change is required.

Activities of Daily Living↗
PubMed2004

Control of prehension in hemiparetic cerebral palsy: similarities and differences between the ipsi- and contra-lesional sides of the body.

This study aimed at broadening our insight into ipsi- and contra-lesional control of prehension after unilateral brain damage. Six male adults with hemiparetic cerebral palsy (mean age 17 years 3 months, SD 15 months) performed unrestricted grasping of discs that differed in size (40, 60, and 80mm in diameter) and which were placed at different distances from the participants (150mm and 30mm). A precalibrated Optotrak 3020 system was used for recording motion. Kinematics of the transport and grasp component, and hand orientation at the moment of grasping, were determined. A marker on the wrist was used to calculate the kinematics of the transport component. The distance between the markers on the index finger and thumb was used for the calculation of the grasp component. Kinematic variables of the transport and grasp component were remarkably similar between both sides of the body. However, with the contra-lesional side, more time was spent in contact with the object before it was lifted, and movements were performed less fluently compared with the ipsi-lesional side. Maximum grasp aperture was attained very late during reaching. For final hand orientation, results showed a large standard deviation both within and between participants. These findings show that, despite the ostensible awkward prehension movements of the contra-lesional side (slowness and decreased fluency), similarities in the kinematics between both sides of the body are present, which may be indicative of intact central control of the movement. The results of variant final hand orientation, combined with the relative late occurrence of peak aperture, suggest that these participants encounter difficulties with forward planning and may use a step-by-step control strategy.

Adolescent↗
PubMed2002

Evidence of an early information processing speed deficit in unipolar major depression.

BACKGROUND: Slowing of the speed of information processing has been reported in geriatric depression, but it is not clear if the impairment is present in younger patients, if motor retardation is responsible, or if antidepressant medications play a role. METHOD: Twenty unmedicated unipolar depressed inpatients were compared with 19 medicated depressed in-patients and 20 age-, sex- and verbal IQ-matched controls on inspection time (IT), a measure of speed of information processing that does not require a speeded motor response. We also examined the relationship between IT and current mood and length of depressive illness. RESULTS: Unmedicated depressed patients showed slowing of information processing speed when compared to both medicated depressed patients and controls. The latter two groups were not significantly different from each other. Slowing of IT was not associated with current mood, but was negatively correlated with length of illness since first episode. No differences in IT were found between patients receiving medication with anticholinergic effects and patients receiving medication with no anticholinergic effects. CONCLUSIONS: The findings indicate that unipolar depression is associated with a slowing of speed of information processing in younger patients who have not received antidepressant medication. This does not appear to be a result of motor slowing.

Adult↗
PubMed1988

Size-difference thresholds after lesions of thalamic visual nuclei in pigeons.

Nucleus rotundus and nucleus dorsolateralis posterior (DLP) are the thalamic components of two parallel pathways within the tectofugal division of the pigeon visual system. An earlier study (Hodos, Weiss & Bessette, 1986) had shown that lesions in direct telencephalic recipients of projections from rotundus and DLP produced postoperative elevations in size-difference thresholds only if the lesion included both structures. What was not revealed by their study was whether the integrity of both thalamic components is necessary for pigeons to discriminate small differences in the size of stimuli or whether the birds could still make the discrimination with only one of the two nuclei intact. This question was particularly important because no prior behavioral evidence existed to indicate that DLP plays a role in visual information processing. Therefore, 14 pigeons were tested preoperatively using a variant of the method of constant stimuli to determine the smallest difference between the size of two annuli that the subjects could discern. The comparison stimuli, which were presented in a successive discrimination procedure, ranged from 3.5-15 mm in diameter. After surgery, in which lesions were placed bilaterally in rotundus, DLP, or both structures, the subjects' size-difference thresholds were again determined. Combined lesions of rotundus and DLP resulted in impaired psychophysical performance. The postoperative behavior was characterized by initial elevations in threshold followed by a gradual improvement in performance. Some birds returned to their preoperative level. By comparison, subjects with lesions in rotundus or DLP alone showed an immediate return to their preoperative sensitivity level. These results indicate that both nuclei can process information about the size of visual stimuli. Moreover, the processing that occurs within either nucleus is sufficient for the pigeon to discriminate size differences. The present experiment provides the first behavioral evidence that DLP participates in visual information processing.

Animals↗
PubMedDate not supplied

Limulus vision in the ocean day and night: effects of image size and contrast.

Male horseshoe crabs, Limulus polyphemus, use their eyes to locate mates day and night. We investigated their ability to detect targets of different size and contrast in a mating area of Buzzards Bay, Cape Cod, MA. We found that males can see large, high-contrast targets better than small, low-contrast ones. For targets of the same size, animals must be about 0.1 m closer to a low-contrast target to see it as well as a high-contrast one. For targets of the same contrast, animals must be approximately 0.2 m closer to a small target to see it as well as one twice as large. A decrease of 0.05 steradians in the size of the retinal image of a target can be compensated by a four-fold increase in contrast. About 60% of the animals detect black targets subtending 0.110 steradians (equivalent to an adult female viewed from about 0.56 m), while only 20% detect targets subtending 0.039 steradians. This study shows that horseshoe crabs maintain about constant contrast sensitivity under diurnal changes in light intensity in their natural environment. As a consequence of circadian and adaptive mechanisms in the retina, male horseshoe crabs can detect female-size objects about equally well day and night.

Adaptation, Ocular↗
PubMedDate not supplied

Dark rearing reveals the mechanism underlying stimulus size tuning of superior colliculus neurons.

Neurons in the superficial layers of the midbrain superior colliculus (SC) exhibit distinct tuning properties for visual stimuli, but, unlike neurons in the geniculocortical visual pathway, most respond best to visual stimuli that are smaller than the classical receptive field (RF). The mechanism underlying this size selectivity may depend on the number and pattern of feedforward retinal inputs and/or the balance between inhibition and excitation within the RF. We have previously shown that chronic blockade of NMDA receptors (NMDA-R), which increases the convergence of retinal afferents onto SC neurons, does not alter size selectivity in the SC. This suggests that the number of retinal inputs does not determine size selectivity. Here we show, using single unit extracellular recordings from the SC of normal hamsters, that size selectivity in neurons selective for small stimulus size is correlated with the strength of inhibition within the RF. We also show that dark rearing causes concomitant reductions in both inhibition and size selectivity. In addition, dark rearing increases the percentage of neurons non-selective for stimulus size. Finally, we show that chronic blockade of NMDA-R, a procedure that does not alter size tuning, also does not change the strength of inhibition within the RF. Taken together, these results argue that inhibition within the RF underlies selectivity for small stimulus size and that inhibition must be intact for size tuning to be preserved after developmental manipulations of activity. In addition, these results suggest that regulation of the balance between excitation and inhibition within the RF does not require NMDA-R activity but does depend on visual experience. These results suggest that developmental experience influences neural response properties through an alteration of inhibitory circuitry.

2-Amino-5-phosphonovalerate↗
PubMedDate not supplied

A high frequency resonance in the responses of retinal ganglion cells to rapidly modulated stimuli: a computer model.

Brisk Y-type ganglion cells in the cat retina exhibit a high frequency resonance (HFR) in their responses to large, rapidly modulated stimuli. We used a computer model to test whether negative feedback mediated by axon-bearing amacrine cells onto ganglion cells could account for the experimentally observed properties of HFRs. Temporal modulation transfer functions (tMTFs) recorded from model ganglion cells exhibited HFR peaks whose amplitude, width, and locations were qualitatively consistent with experimental data. Moreover, the wide spatial distribution of axon-mediated feedback accounted for the observed increase in HFR amplitude with stimulus size. Model phase plots were qualitatively similar to those recorded from Y ganglion cells, including an anomalous phase advance that in our model coincided with the amplification of low-order harmonics that overlapped the HFR peak. When axon-mediated feedback in the model was directed primarily to bipolar cells, whose synaptic output was graded, or else when the model was replaced with a simple cascade of linear filters, it was possible to produce large HFR peaks but the region of anomalous phase advance was always eliminated, suggesting the critical involvement of strongly non-linear feedback loops. To investigate whether HFRs might contribute to visual processing, we simulated high frequency ocular tremor by rapidly modulating a naturalistic image. Visual signals riding on top of the imposed jitter conveyed an enhanced representation of large objects. We conclude that by amplifying responses to ocular tremor, HFRs may selectively enhance the processing of large image features.

Action Potentials↗
PubMed2006

The effect of content and physical properties of affective pictures on emotional responses.

The aim of this research was to study the influence of both the emotional content and the physical characteristics of affective stimuli on the psychophysiological, behavioral and cognitive indexes of the emotional response. We selected 54 pictures from the IAPS, depicting unpleasant, neutral, and pleasant contents, and used two picture sizes as experimental conditions (120 x 90 cm and 52 x 42 cm). Sixty-one subjects were randomly assigned to each experimental condition. We recorded the startle blink reflex, skin conductance response, heart rate, free viewing time, and picture valence and arousal ratings. In line with previous research (e.g., Bradley, Codispoti, Cuthbert, and Lang, 2001), our data showed an effect of the affective content on all the measurements recorded. Importantly, effects of the size of the affective pictures on emotional responses were not found, indicating that the emotional content is more important than the formal properties of the stimuli in evoking the emotional response.

Adolescent↗
PubMed2000

An evaluation of food photographs as a tool for quantifying food and nutrient intakes.

OBJECTIVE: To evaluate the errors incurred by young adults using single portion size colour food photographs to quantify foods and nutrients consumed at six meals on two non-consecutive days. DESIGN: Breakfast menus remained the same for the 2 days; but lunch and dinner menus varied. The amounts of food eaten by individuals were determined by weighing individual serving dishes pre- and post-consumption. The day after eating, all foods consumed were quantified in terms of fractions or multiples of the amounts shown in the food photographs. SUBJECTS: Thirty adult volunteers (15 male, 15 female), aged 18-36 years, completed the protocol for day one; 27 (90%) completed day two. RESULTS: Some foods were more difficult to quantify accurately than others. The largest error range was -38. 9% to +284.6% (cheese), whereas the smallest errors were incurred for juice (-21.5% to +34.6%, day one). All subjects who consumed muesli (day one) overestimated (+3.7% to +113.7%). No other foods were consistently over- or underestimated. For foods consumed at breakfast by the same subjects on both days, individual estimation errors were inconsistent in magnitude and/or direction. At the group level, most nutrients were estimated to within +/-10% of intake; exceptions were thiamin (+10.5%, day one) and vitamin E (-10.1%, day one; -15.3%, day two). Between 63% and 80% of subjects were correctly classified into tertiles on the basis of estimated intakes. CONCLUSIONS: Despite some large food quantification errors, single portion size food photographs were effective when used to estimate nutrient intakes at the group level. It remains to be established whether, under the conditions used in this study, more photographs per food would improve estimates of nutrient intake at the individual level.

Adolescent↗
PubMed2005

A blank look in reading: the effect of blank space on the identification of letters and words during reading.

Two experiments investigated the effect of visual blank space on reading by varying the amount of interletter and interline blank space in prose passages. Increasing interletter blank spacing slowed the reading process overall, presumably because it disrupted the unitization of words and word identification, but it also improved the identification of the letters within words. By contrast, increasing interline blank spacing sped up the reading process overall, while also improving the identification of words and the letters within words, presumably because the extra spacing reduced the amount of visual information that was processed during reading. The latter finding supports the conclusion that information from surrounding lines of single-spaced text may interfere with reading.

Comprehension↗
PubMed2005

Perceptual effects and recollective experience in face recognition.

Four experiments were conducted investigating the effect of size congruency on facial recognition memory, measured by remember, know and guess responses. Different study times were employed, that is extremely short (300 and 700 ms), short (1,000 ms), and long times (5,000 ms). With the short study time (1,000 ms) size congruency occurred in knowing. With the long study time the effect of size congruency occurred in remembering. These results support the distinctiveness/ fluency account of remembering and knowing as well as the memory systems account, since the size congruency effect that occurred in knowing under conditions that facilitated perceptual fluency also occurred independently in remembering under conditions that facilitated elaborative encoding. They do not support the idea that remember and know responses reflect differences in trace strength.

Adolescent↗
PubMed1996

Dynamic touch.

People can perceive a number of spatial and other properties of objects, without the benefit of vision, simply by wielding and hefting the objects. A variety of recent experiments are reported, showing that in this kind of touching, which is closely connected with the states of muscles, the nervous system cleverly exploits the physics of rotations.

Discrimination Learning↗
PubMed1997

Interpreting infant looking: the event set x event set design.

Theory, data, and mathematical models presented suggest that perceptual processing may be crucial in young infant cognition. Prior results indicating early or innate physical knowledge are reinterpreted. Assumptions that young infants use higher level cognitive processes to infer, reason, believe, and so on are challenged in favor of perceptual processes and the effects of novelty and familiarity. The 2-test habituation design that compares looking at the "possible" with looking at the "impossible" and the problems of that design are considered. The authors' approach, based on regression analysis of Event Set X Event Set factorial designs, eliminates those problems, refines gauging the contribution of various variables, quantifies these contributions with standard parameter estimation, unconfounds the crucial variables, and tests which variables are responsible for looking time differences. Data are presented that support the perceptual processing perspective. Application of the new design to 2 seminal studies of infant cognition are suggested.

Attention↗
PubMed1999

Early fraction calculation ability.

Three- to 7-year-olds' ability to calculate with whole-number, fraction, and mixed-number amounts was tested using a nonverbal task in which an amount was displayed and then hidden (J. Huttenlocher, N. C. Jordan, & S. C. Levine, 1994). Next, an amount was added to or subtracted from the hidden amount. The child's task was to determine the hidden amount that resulted from the transformation. Although fraction problems were more difficult than whole-number problems, competence on all problem types emerged in the early childhood period. Furthermore, there were striking parallels between the development of whole-number and fraction calculation. This is inconsistent with the hypothesis that early representations of quantity promote learning about whole numbers but interfere with learning about fractions (e.g., R. Gelman, 1991; K. Wynn, 1995, 1997).

Age Factors↗