Piaget's 3-mountains task with impossible options: Sighted, blindfolded, early and late blind participants.

In Piaget's 3-mountains task, 3D objects - a cube, cone and sphere - sit on a square tabletop. They are portrayed in 2D pictures as elevations (projections to the sides) such as one with a square on the left, a triangle in the middle and a circle on the right. Three objects offer six elevations, of which four are possible and two impossible. The possibles are elevations from the sides of the table - front, left, right and rear. In the impossibles, an object in the corner of the table is shown in the middle of an elevation. Sighted, sighted-blindfolded, early- and late-blind adults judged the elevations as to side of the table or impossible. The results suggest similar spatial abilities across groups. The impossible options had mid-range accuracy for all groups, with reaction times like possible options. The sighted and blind participants may consider possible and impossible options sequentially, one item at a time.

Foreshortening increases apparent angles.

The hypothesis that perspective foreshortening leads to errors in the visual perception of angles, was tested in four experiments. An oblique to a z-dimension line was presented (a) on the ground in Experiments 1 and 2, and (b) on a wall in Experiments 3 and 4. Observers judged the acute angle between the oblique and the z-line. Foreshortening increased with the oblique's distance along the z-line and, in Experiments 2 and 4, shorter distances from the eye to the ground or wall. As distance and eye-height vary, so does the target's slant to the line of sight. We argue the apparent angles between the lines increased with foreshortening because vision underestimates the fast rate of foreshortening with elevation compared with the slower rates in azimuth.

Foreshortening produces errors in the perception of angles pictured as on the ground.

Observers viewed pictures of a simulated ground plane and judged the orientation of lines pictured as lying on the ground. We presented three lines at a time and manipulated three factors: (1) the declination of the lines below the horizon (depicting distance to the target angles), (2) their length, and (3) whether or not they converged to a point on the horizon. Only the first factor had a substantial effect on these errors. We conclude that perspective foreshortening in pictures produces errors in perceived 3-D orientation. Our explanation is based on the different rates of change of elevation and azimuth with distance.

Pointing to azimuths and elevations of targets: blind and blindfolded-sighted.

Three groups of observers pointed to target circles in a path on the ground, in two parallel rows. Participants in one group viewed the circles and then pointed blindfolded. Those in a second group were blindfolded and then touched the circles with a stick while walking past them. Volunteers in the third group were blind adults, a diverse group, who also used a stick to detect the circles. For all three groups, as distance to the circles increased, pointing azimuths shrank and elevations increased. We suggest that directions to targets on major environmental surfaces may be appreciated similarly by the blind and sighted. We challenge the assumption that the principle of convergence to the horizon, available through vision because of the way in which visual angle decreases on the retina, is not available through touch.

Picture surface illusion: small effects on a major axis.

Perception of 2-D ellipses on a picture surface is inaccurate-if the ellipses depict circles that are tilted in 3-D, receding from the viewer (Hammad, Kennedy, Juricevic, & Rajani, 2008a, Perception, 37, 504-510). Notably, the minor axis of the ellipse is seen as larger than is true. This illusory effect could be due to the simultaneous presence of optical information for the 2-D ellipse and optical information for the 3-D tilted circle. The optical information for the circle may bias vision's use of the optical information for the ellipse. This theory predicts that illusory effects should occur on the major axis as well as the minor axis; but, we argue, the major axis effect should be smaller than the minor axis effect. We confirm the prediction. Observers looked at target ellipses depicting tops of tilted cylinders. In one experiment observers chose a match for the target from choice sets of seven 2-D ellipses. In the second, observers used the method of adjustment. Both axes were overestimated, the minor axis more than the major, as the theory suggested. We point out that the relative size of the effects matters to the theory, and so the small effect counts for a lot.

Mirror image arm used in monocular, binocular, and blindfolded pointing.

Observers were instructed to point with their right arm to a mirror image of their left shoulder. Instead of pointing to the target with their real arm, they occluded the target with their mirror-imaged finger, and their real finger pointed off to the left side of the target, facts that came as a surprise to them in debriefing. The occlusion by a mirror image finger was not done to avoid double images, since it occurred in monocular conditions. That it is due to planning before pointing can be inferred from the fact that it occurred in blindfolded conditions.

Elevation easier than plan for sighted and early-blind adults in a perspective-taking task.

Plans show shapes of objects from above, and represent both their left-right order and their order in the z-dimension (the distance of the objects). Elevations show only the vertical shapes of objects arranged from left to right. Plans, having more spatial information, may be more difficult for participants to construct. Results from a study with sighted, sighted-blindfolded, and early-blind participants on Piaget's perspective-taking three-mountain task support this hypothesis. The plan task was judged more difficult than the elevation task even when participants performed with the same level of accuracy on both tasks. In visual and tactile tasks, amount of spatial-order information may determine difficulty, rather than plan versus elevation per se.

When age is irrelevant: distractor inhibition and target activation in priming of pop-out.

OBJECTIVES: Recent research suggests that inhibition at early stages of visual processing may be age invariant. We test this proposal using a priming of pop-out (PoP) measure developed by Lamy, Antebi, Aviani, and Carmel (2008. Priming of pop-out provides reliable measures of target activation and distractor inhibition in selective attention. Vision Research, 48, 30-41. doi:10.1016/j.visres.2007.10.009). In PoP, a unique item, which visually "pops-out" in a field of distractors, grabs our attention faster when its defining feature (e.g., color red) repeats across trials and slower when distractor- and target-defining features switch between trials. Here, we explore whether the processes underlying PoP, which prevent access to distractors and facilitate access to the singleton, remain intact with age. METHOD: Participants faced a display of circles and judged the direction of a letter T inscribed within a uniquely colored circle. RESULTS: All underlying components of PoP were present in older and younger adults. Participants revealed distractor inhibition by responding faster to a color singleton when the color of surrounding distractors repeated and slower when the singleton assumed the color of distractors from the previous trial. DISCUSSION: Our findings suggest that the inhibitory processes underlying PoP remain intact with age.

Pivots for pointing: visually-monitored pointing has higher arm elevations than pointing blindfolded.

Observers pointing to a target viewed directly may elevate their fingertip close to the line of sight. However, pointing blindfolded, after viewing the target, they may pivot lower, from the shoulder, aligning the arm with the target as if reaching to the target. Indeed, in Experiment 1 participants elevated their arms more in visually monitored than blindfolded pointing. In Experiment 2, pointing to a visible target they elevated a short pointer more than a long one, raising its tip to the line of sight. In Experiment 3, the Experimenter aligned the participant's arm with the target. Participants judged they were pointing below a visually monitored target. In Experiment 4, participants viewing another person pointing, eyes-open or eyes-closed, judged the target was aligned with the pointing arm. In Experiment 5, participants viewed their arm and the target via a mirror and posed their arm so that it was aligned with the target. Arm elevation was higher in pointing directly.