Minimizing rivalry in San Miniato

A workshop on binocular rivalry and perceptual ambiguity was held in San Miniato, Italy, on 12-15 June, 2002.     

Cognitive Task Analysis for Implicit Knowledge About Visual Representations With Similarity Learning Methods

Visual representations are prevalent in STEM instruction. To benefit from visuals, students need representational competencies that enable them to see meaningful information. Most research has focused on explicit conceptual representational competencies, but implicit perceptual competencies might also allow students to efficiently see meaningful information in visuals. Most common methods to assess students’ representational competencies rely on verbal explanations or assume explicit attention. However, because perceptual competencies are implicit and not necessarily verbally accessible, these methods are ill‐equipped to assess them. We address these shortcomings with a method that draws on similarity learning, a machine learning technique that detects visual features that account for participants’ responses to triplet comparisons of visuals. In Experiment 1, 614 chemistry students judged the similarity of Lewis structures and in Experiment 2, 489 students judged the similarity of ball‐and‐stick models. Our results showed that our method can detect visual features that drive students’ perception and suggested that students’ conceptual knowledge about molecules informed perceptual competencies through top‐down processes. Furthermore, Experiment 2 tested whether we can improve the efficiency of the method with active sampling. Results showed that random sampling yielded higher accuracy than active sampling for small sample sizes. Together, the experiments provide the first method to assess students’ perceptual competencies implicitly, without requiring verbalization or assuming explicit visual attention. These findings have implications for the design of instructional interventions that help students acquire perceptual representational competencies.     

Role of spatial and temporal coincidence in depth organization

The linking of spatial information is essential for coherent space perception. A study is reported of the contribution of temporal and spatial alignment for the linkage of spatial elements in terms of depth perception. Stereo half-images were generated on the left and right halves of a large-screen video monitor and viewed through a mirror stereoscope. The half-images portrayed a black vertically oriented bar with two brackets immediately flanking this bar and placed in crossed or uncrossed disparity relative to the bar. A pair of thin white 'bridging lines' could appear on the black bar, always at zero disparity. Brackets and bridging lines could be flickered either in phase or out of phase. Observers judged whether the brackets appeared in front of or behind the black bar, with disparity varied. Compared to conditions when the bridging lines were absent, depth judgments were markedly biased toward "in front" when bridging lines and brackets flashed in temporal phase; this bias was much reduced when the bridging lines and brackets flashed out of phase. This biasing effect also depended on spatial offset of lines and brackets. However, perception was uninfluenced by the lateral separation between object and brackets.     

The development of same and different judgments

Junior kindergarten children, third-grade children, and college students were given a simultaneous pattern discrimination task, with simple and complex patterns, under either unlimited or limited (150 msec) viewing time. Under unlimited viewing, RTs to same patterns were faster than to different patterns for younger children and older males. Under limited viewing, same and different RTs were equivalent, but more errors were made in judging different patterns by all age groups. The RTs were longer to complex than to simple patterns, but the increase was differentially less for the youngest Ss, especially on same pairs. Since this age difference was found under both limited and unlimited viewing, it was not attributable to age differences in perceptual scanning strategies. The same-different asymmetry in RT under unlimited viewing and in error rate under limited viewing confirms across a wide age range previous findings with adults using codable stimuli. A two-process model for same and different judgments appears to be required, although young children may have had a response bias for same in Expt II.     

Children's binary prediction of partially learnable sequences followed by an all-correct procedure

Six groups of 20 subjects each were run individually in a binary prediction situation with each alternative occurring equally often. Two age groups were employed; subjects were either in second or sixth grades. For one-third of the subjects at each age level, the events occurred in runs of either two or six; another third observed events which occurred in runs of either five or six; the other subjects received a random sequence of events. All subjects then received an additional 50 trials in which every prediction was correct. The results indicated some sensitivity to run length characteristics. Fewer errors of all types were made in the prediction of 5–6 sequences. The verbal reports and all-correct trial protocols revealed that at least the sixth graders employed some simple run length structure rules, although many instances of runs other than those presented in training occurred, showing much processing error. The results were discussed in terms of a general limited-capacity model of information-processing.     

Effects of time and event uncertainty upon sequential information processing

Two experiments were conducted to investigate the psychological refractory period (PRP), a delay induced into the second of two reaction times (RT) when the interstimulus interval (ISI) is short. In Experiment1, time and event uncertainty were factorially varied by providing or not providing S with foreknowledge of the ISI and the order in which the two events would occur, respectively. ISIs of0, 50, 100, 200, and400 msec were used. Time and event uncertainty produced independent degradation of both RTs. Also, the second RT (RT ₂ ) was delayed at50 msec ISI when both time and event certainty were present. Experiment 2 attempted to replicate this latter finding using ISIs of0, 25, 50, 75, and100 msec. Delays in RT ₂ were found for the middle three values of ISI. These results were interpreted as supporting a modified single channel theory of the PRP.     

Does direction of walking impact binocular rivalry between competing patterns of optic flow?

When dissimilar monocular images are viewed simultaneously by the two eyes, stable binocular vision gives way to unstable vision characterized by alternations in dominance between the two images in a phenomenon called binocular rivalry. These alternations in perception reveal the existence of inhibitory interactions between neural representations associated with conflicting visual inputs. Binocular rivalry has been studied since the days of Wheatstone, but one recent strategy is to investigate its susceptibility to influences caused by one’s own motor activity. This paper focused on the activity of walking, which produces an expected, characteristic direction of optic flow dependent upon the direction of one’s walking. In a set of experiments, we employed virtual reality technology to present dichoptic stimuli to observers who walked forward, backward, or were sitting. Optic flow was presented to a given eye, and was sometimes congruent with the direction of walking, sometimes incongruent, and sometimes random, except when the participant was sitting. Our results indicate that, while walking had a reliable influence on rivalry dynamics, the predominance of congruent or incongruent motion did not.