Institute of Optometry and Visual Science

The authors examined center-surround effects for motion perception in human observers. The magnitude of the motion aftereffect (MAE) elicited by a drifting grating was measured with a nulling task and with a threshold elevation procedure. A surround grating of the same spatial frequency, temporal frequency, and orientation significantly reduced the magnitude of the MAE elicited by adaptation to the center grating. This effect was bandpass tuned for spatial frequency, orientation, and temporal frequency. Plaid surrounds but not contrast-modulated surrounds that moved in the same direction also reduced the MAE. These results provide psychophysical evidence for center-surround interactions analogous to those previously observed in electrophysiological studies of motion processing in primates. Collectively, these results suggest that motion processing, similar to texture processing, is organized for the purpose of highlighting regions of directional discontinuity in retinal images.

By comparing real observers to an ideal observer, previous studies have found that the detection of static patterns is limited by internal noise and by imperfect sampling efficiency. We developed and applied ideal observer models for the detection, discrimination, and summation of oppositely drifting gratings in Gaussian white noise. The three tasks share a common source of internal noise. The sampling efficiencies were on the order of 1-2% except for much lower efficiency in direction discrimination for faster moving gratings. The efficiency of direction discrimination relative to detection systematically declines as the speed is increased from 1 to 6 Hz. These results suggest that observers use mismatched filters tuned to slow speeds regardless of the signal speed. Human visual motion sensing appears to use distorted representations of the incoming signals, and this distortion is a major limitation to visual performance.

We examine how local direction signals are combined to compute the focus of radial motion (FRM) in random dot patterns and examine how this process changes across the visual field. Equivalent noise analysis showed that a loss in FRM accuracy was largely attributable to an increase in local motion detector noise with little or no change in efficiency across the visual field. The minimum separation for discriminating the foci of two overlapping optic flow patterns increased in the periphery faster than predicted from the resolution for a single FRM. This behavior requires that observers average numerous local velocities to estimate the FRM, which enables resistance to internal and external noise and endows the system with the property of position invariance. However, such pooling limits the precision with which multiple looming objects can be discriminated, especially in the peripheral visual field.

Primary open angle glaucoma (POAG) is a leading cause of irreversible adult blindness and is characterized by progressive optic neuropathy and constriction of the visual field. Behavioral tests for POAG target retinal ganglion cell (RGC) classes that have reduced redundancy or that might be selectively damaged, but these tests cannot differentiate dysfunctional from nonfunctional RGC inputs to motion sensors. In this study, a signal-to-noise motion-sensitivity task was used to investigate the sources of motion-sensitivity loss in patients with POAG. An equivalent noise paradigm was used to investigate sensitivity to the direction of radial optic flow patterns across the visual field in visually normal observers and patients with POAG. Internal noise and sampling efficiency were estimated from the direction of heading contrast-discrimination thresholds as a function of the level of added external noise. Contrast sensitivity to optic flow fell with retinal eccentricity for all observe...

By comparing real observers to an ideal observer, previous studies have found that the detection of static patterns is limited by internal noise and by imperfect sampling efficiency. We developed and applied ideal observer models for the detection, discrimination, and summation of oppositely drifting gratings in Gaussian white noise. The three tasks share a common source of internal noise. The sampling efficiencies were on the order of 1-2% except for much lower efficiency in direction discrimination for faster moving gratings. The efficiency of direction discrimination relative to detection systematically declines as the speed is increased from 1 to 6 Hz. These results suggest that observers use mismatched filters tuned to slow speeds regardless of the signal speed. Human visual motion sensing appears to use distorted representations of the incoming signals, and this distortion is a major limitation to visual performance.

A functionally optimized housing development designed to meet the demands in different phases of living (universal design) may result in the elderly living longer in their own homes. In this study a total of 165 healthy persons were included out of a total of approximately 320 persons turning 75 years of age in 2009 living in Drammen municipality. They went through a quantitative, questionnaire-based interview (including VAS and SF-36) and 20 participants were then selected for a qualitative in depth interview. The lighting conditions in the kitchen, living room, bathroom, bedroom and staircase were measured according to a simplified procedure. The overall lighting conditions were evaluated to be rather low, with means between 35 and 121 Lux, but the quantitative interviews showed that on most questions the scores were rather low, indicating that the overall thriving is good regardless of rather low lighting values.

Global motion perception matures during childhood and involves the detection of local directional signals that are integrated across space. We examine the maturation of local directional selectivity and global motion integration with an equivalent noise paradigm applied to direction discrimination. One hundred and three observers (6-17 years) identified the global direction of motion in a 2AFC task. The 88 central stimuli consisted of 100 dots of 10% Michelson contrast moving 2.88/s or 9.88/s. Local directional selectivity and global sampling efficiency were estimated from direction discrimination thresholds as a function of external directional noise, speed, and age. Direction discrimination thresholds improved gradually until the age of 14 years (linear regression, p , 0.05) for both speeds. This improvement was associated with a gradual increase in sampling efficiency (linear regression, p , 0.05), with no significant change in internal noise. Direction sensitivity was lower for dots moving at 2.88/s than at 9.88/s for all ages (paired t test, p , 0.05) and is mainly due to lower sampling efficiency. Global motion perception improves gradually during development and matures by age 14. There was no change in internal noise after the age of 6, suggesting that local direction selectivity is mature by that age. The improvement in global motion perception is underpinned by a steady increase in the efficiency with which direction signals are pooled, suggesting that global motion pooling processes mature for longer and later than local motion processing.

Studentaktive vurderingsformer i norsk laerer-og optometriutdanning Sammendrag Medstudentvurdering 1 er en form for studentarbeid som er blitt tatt i bruk og forsket på i større omfang internasjonalt enn nasjonalt. Her presenteres to casestudier med bruk av medstudentvurdering fra to ulike profesjonsutdanninger i Norge: optikerutdanningen ved avdeling for optometri-og synsvitenskap 2 og laererutdanningen ved avdeling for laererutdanning ved Høgskolen i Buskerud. Kombinasjonen medstu-dentvurdering og egenvurdering ble også prøvd ut. Artikkelen belyser erfaringer og utfordringer i forbindelse med planlegging og gjennomfø-ring samt analyse og diskusjon av studentenes evaluering av medstu-dentvurdering. 3 Innledning Kvalitetsreformen (KUF, 2000/2001) forutsetter at alternative vurde-rings-og tilbakemeldingsformer vil bli innført istedenfor eller i til-legg til tradisjonell skoleeksamen som kun munner ut i en karakter. I evalueringen av Kvalitetsreformens undervisnings-og vurderingsfor-m...