Cue combination for 3D location judgements

Cue combination rules have often been applied to the perception of surface shape but not to judgements of object location. Here, we used immersive virtual reality to explore the relationship between different cues to distance. Participants viewed a virtual scene and judged the change in distance of an object presented in two intervals, where the scene changed in size between intervals (by a factor of between 0.25 and 4). We measured thresholds for detecting a change in object distance when there were only 'physical' (stereo and motion parallax) or 'texture-based' cues (independent of the scale of the scene) and used these to predict biases in a distance matching task. Under a range of conditions, in which the viewing distance and position of the tarte relative to other objects was varied, the ration of 'physical' to 'texture-based' thresholds was a good predictor of biases in the distance matching task. The cue combination approach, which successfully accounts for our data, relies on quite different principles from those underlying geometric reconstruction

A demonstration of 'broken' visual space

It has long been assumed that there is a distorted mapping between real and ‘perceived’ space, based on demonstrations of systematic errors in judgements of slant, curvature, direction and separation. Here, we have applied a direct test to the notion of a coherent visual space. In an immersive virtual environment, participants judged the relative distance of two squares displayed in separate intervals. On some trials, the virtual scene expanded by a factor of four between intervals although, in line with recent results, participants did not report any noticeable change in the scene. We found that there was no consistent depth ordering of objects that can explain the distance matches participants made in this environment (e.g. A > B > D yet also A < C < D) and hence no single one-to-one mapping between participants’ perceived space and any real 3D environment. Instead, factors that affect pairwise comparisons of distances dictate participants’ performance. These data contradict, more directly than previous experiments, the idea that the visual system builds and uses a coherent 3D internal representation of a scene

Sekundært glaukom som følge av sprettertskade: diagnostisert et halvt århundre senere

Sekundært glaukom som følge av stumpt traume mot øyet forekommer relativt sjelden i optometrisk praksis. Denne typen glaukom kan oppstå etter korttid eller flere tiår senere. Kasuistikken presenterer en mann som i en alderav 57 år ble diagnostisert med traumatisk glaukom, trolig som følge av ensprettertulykke som ni-åring. Skaden medførte betydelig redusert syn på det venstre øyet, men bortsett fra dette hadde han ikke hatt noen øye- eller synsplager. Pasienten hadde aldri vært til synsundersøkelse i voksen alder, og han fungerte godt med ferdigbriller til nærarbeid. Alle undersøkelser på høyre øye viste normale funn. På venstre øye ble det funnet redusert visus, irisdialyse inferionasalt, angle recession, forhøyet intraokulært trykk og randekskavert papille. Pasienten ble henvist til øyelege som bekreftet at pasienten hadde unilateralt glaukom. Kasuistikken tar for seg situasjoner der sekundært glaukom fra stumpt traume kan oppstå, hvilke okulære tegn som kan være tilstede og hvilke undersøkelser som bør gjøres. Videre diskuteres viktigheten av oppfølging av pasienter som har hatt traume mot øyne og hode

Investigating representation of visual space for freely moving participants in a virtual expanding room

One of the important and unsolved questions in vision research is how space is represented. Despite extensive research from a variety of disciplines this topic is still poorly understood and, at present, there is no theory that can provide a complete explanation. The traditional view on space representation is a geometric one that assumes a one-to-one mapping between physical and perceived space, but much of the current evidence points towards other solutions. For example, it has been proposed that there may be no single visual representation of a 3D scene that can account for performance in all tasks, suggesting that space representation may take a looser form without a globally consistent map of space. The studies described in this thesis provide evidence that challenges the idea of a single internal representation of space by exploring size and distance judgements under a range of different conditions in a virtual expanding room. In this environment, participants viewed the scene binocularly through a wide field of view head mounted display. They were allowed to move and were consequently provided with veridical information about the scene also from their own movements. Importantly, the scene expanded or contracted four-fold during experiments, giving a unique opportunity to explore how different distance cues contribute to size and distance judgements when biases in both judgements were very large. The available cues were set in conflict: one type of cue, based on stereopsis and motion parallax, gave a veridical signal of the change in the scene, whereas another type of cue was unaffected by the expansion of the scene and, hence, signalled that the room remained constant. The most striking result is that the perceived location of objects does not always follow a transitive ordering with respect to physical space, which is incompatible with a one-to-one mapping between perceived and physical space. Instead, the results can be better explained by a cue combination model. This approach has not previously been used for object location, but was here successfully applied for a range of conditions even when there was a large conflict between the distances signalled by the contributing cues. Further, it appears that perceived size and perceived distance are not based on a single estimate of distance, demonstrating the lack of internal consistency from a different angle. Overall, these experiments provide results that are difficult to reconcile with a model based on geometric reconstruction and suggest that the visual system does not have a single internal representation of space.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Vision status of children aged 7–15 years referred from school vision screening in Norway during 2003–2013: a retrospective study

Background: Undetected vision problems is an important cause of reduced academic achievement, performance in everyday life and self-esteem. This receives little attention in national health care services in Norway even though most of these vision problems are easily correctable. There are no published data on how many Norwegian schoolchildren are affected by correctable vision problems. This study aims to determine the vision status in primary and secondary schoolchildren referred from vision screening during the 10 year period of 2003–2013. Methods: Of the 1126 children (15%) aged 7–15 years referred to the university eye clinic by the school screening program, all 782 who attended the eye clinic were included in the study. Patient records were retrospectively reviewed with regard to symptoms, refractive error, best corrected visual acuity (BCVA) of logMAR, binocular vision, ocular health and management outcomes. Results: Previously undetected vision problems were confirmed in 650 (83%) of the children. The most frequent outcomes were glasses (346) or follow-up (209), but types of treatment modalities varied with age. Mean refractive errors were hyperopic for all age groups but reduced with age (ANOVA, p 0.05). Mean logMAR BCVAs were better than 0.0 and improved with age (ANOVA, p < 0.001). The most prevalent symptoms were headaches (171), near vision problems (149) and reduced distance vision (107). Conclusions: The vision screening identified children with previously undetected visual problems. This study shows that the types of visual problems varied with age and that most problems could be solved with glasses. Our results stress the importance of regular eye examinations and that vision examinations should be included in primary health care services. Further

Inferring points of subjective equality (PSEs).

<p>Because we ran all the conditions simultaneously, the appropriate distance for the reference squares B and C could not be determined precisely in advance. Instead, two reference distances close to the expected value were chosen and interpolation (or, rarely, extrapolation) used to estimate the PSE that would have been obtained had the reference been positioned at the ‘ideal’ distance (<i>C_A</i>, black arrow). Two reference locations (<i>C_ref1</i> and <i>C_ref2</i>, open arrows) and the corresponding psychometric functions are shown, together with the interpolated curve (black) and inferred PSE (dashed line). See also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033782#pone.0033782.s001" target="_blank">Figure S1</a>.</p

Normalised values of PSE for square D plotted against normalised values of the reference distance.

<p>Zero on the abscissa (<i>x</i>₀) is the vergence angle at the ‘ideal’ reference distance, i.e. the PSE <i>B_A</i> or <i>C_A</i>. The difference between this ‘ideal’ value and the vergence angles of the reference squares (presented at distances <i>B_ref1</i>, <i>B_ref2</i>, <i>C_ref1</i> or <i>C_ref2</i>) was divided by the standard deviation of the psychometric function that gave rise to PSE <i>B_A</i> or <i>C_A</i> (<i>σ_x</i>), so that, in effect, the reference distances are plotted as z-scores (<i>x</i> = (<i>x</i>₁−<i>x</i>₀)/<i>σ_x</i>, where <i>x</i>₁ is the vergence angle of the reference surface and <i>x</i> is the value plotted; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033782#pone.0033782.s005" target="_blank">Procedures S2</a> for details). Similarly, zero on the ordinate is the expected PSE for D if the reference was at the ‘ideal’ distance (the mean of PSE <i>D_B</i> and PSE <i>D_C</i>, expressed as a vergence angle, <i>y</i>₀). The difference between this ‘ideal’ PSE and the actual PSEs measured (<i>D_B1</i>, <i>D_B2</i>, <i>D_C1</i> and <i>D_C2</i>, expressed as a vergence angles, <i>y</i>₁) were divided by the root mean square standard deviation of the psychometric functions (<i>σ_y</i>) that gave rise to PSE (<i>y</i> = (<i>y</i>₁<i>−y</i>₀)/<i>σ_y</i>; see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033782#pone.0033782.s005" target="_blank">Procedures S2</a> for details). As in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033782#pone-0033782-g004" target="_blank">Figure 4</a>, red symbols show data for route A – B – D and blue symbols for the route A – C – D. Different symbols shapes are used for different participants. The red plusses and blue crosses re-plot the interpolated data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0033782#pone-0033782-g004" target="_blank">Figure 4</a> on these relative axes. They are shown at a reference vergence angle of zero, by definition in this plot, since the notional reference is always the ‘ideal’ reference distance (PSE <i>B_A</i> or <i>C_A</i>).</p

Labels used for reference distances and points of subjective equality (PSEs).

<p>Runs were repeated using two different reference distances for square B (i.e. <i>B_ref1</i> or <i>B_ref2</i>) and similarly two values for square C. For points of subjective quality, subscripts indicate the reference square: e.g. <i>B_A</i> refers to the PSE when square B, shown in interval 2, appeared to be at the same distance as square A, shown in interval 1.</p

Four interleaved distance comparisons.

<p>Plan views (left) show how the room remained the same size between intervals (Rows I and IV) or expanded (Rows II and III), not drawn to scale. In each case, the position of the reference square in interval 1 is shown by the dashed line and the comparison square (interval 2) by a solid line. The psychometric functions show the proportion of trials on which the comparison square was judged to be ‘farther away’ than the reference. The arrows show the distance to the reference square (in arc minutes and metres on top and bottom axes, respectively) and the dashed line shows the point of subjective equality (PSE). Plots in the right hand column show participants' biases, i.e. the difference between the reference and the PSE (expressed in arcmin). In most cases, standard error of the PSEs, obtained from the probit fit, are smaller than the size of the markers. Although not shown here, square B and C were each presented at two reference distances (<i>B_ref1</i>, <i>B_ref2</i>, <i>C_ref1</i>, and <i>C_ref2</i>). The reference distances illustrated here are <i>B_ref1</i> and <i>C_ref1</i>. Similarly, the biases for square D shown in red and blue are those obtained with references <i>B_ref1</i> and <i>C_ref1</i>, namely PSE <i>D_B1</i> and <i>D_C1</i> (see text for details).</p