Binocular fusion enhances the efficiency of spot-the-difference gameplay

Binocular luster elicited by isoluminant chromatic stimuli relies on mechanisms similar to those in the achromatic case

The phenomenon of binocular luster can be evoked by simple dichoptic center-surround stimuli showing a luminance contrast difference between the eyes. Previous findings support the idea that this phenomenon is mediated by a low-level conflict mechanism that integrates the monocular signals from different types of contrast detector cells. Also, isoluminant stimuli with different chromatic contrasts between eyes can trigger sensations of luster. Here, we investigate whether the lustrous impression in such purely chromatic stimuli depends on interocular contrast differences and in particular on interocular contrast polarity pairings in a similar way as in the achromatic case. In our experiments, we measured the magnitude of the lustrous response using a series of isoluminant dichoptic center-ring-surround stimuli with varying ring width whose chromatic properties were varied along the red-green and blue-yellow cardinal directions. The trends in the data were very similar to those of our former study with achromatic stimuli, indicating similar mechanisms in both cases. The empirical luster data could also be predicted fairly well by a chromatic version of our interocular conflict model (with overall R2 values between 0.577 and 0.639), for which two different receptive field models were used, simulating the behavior of color-sensitive double-opponent cells in V1.

Success rates, near-response patterns, and learning trends with free-fusion stereograms

Free-fusion stereograms are routinely used for demonstrating various stereoscopic effects. Yet, untrained observers find it challenging to perform this task. This study showed that only less than 1/3rd of sixty-one pre-presbyopic adults with normal binocular vision could successfully free-fuse random-dot image pairs and identify the stereoscopic shapes embedded in these patterns. Another one-third of participants performed the task with poor success rates, while the remaining could not perform the task. There was a clear dissociation of vergence and accommodative responses in participants who were successful with free-fusion, as recorded using a dynamic infrared eye tracker and photorefractor. Those in the unsuccessful cluster either showed strong vergence and accommodation or weak vergence and strong accommodation during the task. These response patterns, however, were specific to the free-fusion task because all these participants generated good convergence/accommodation to real-world targets and to conflicting vergence and accommodative demands stimulated with prisms or lenses. Task performance of the unsuccessful cluster also improved significantly following pharmacological paralysis of accommodation and reached the performance levels of the successful cluster. A minority of participants also appeared to progressively learn to dissociate one of the two directions of their vergence and accommodation crosslinks with repeated free-fusion trials. These results suggest that successful free-fusion might depend upon how well participants generate a combination of volitional and reflex vergence responses to large differences in disparity with conflicting static accommodative demands. Such responses would require that only one direction of the vergence-accommodation crosslinks be active at any given time. The sequence of near-responses could also be learnt through repeated trials to optimize task performance.

A simple model of binocular luster

The dichoptic combination of simple center–surround stimuli showing a contrast difference between eyes can trigger a lustrous impression in the fused percept, particularly when the contrast polarities in the two input images are of opposite sign. Recent developments suggest that the phenomenon of binocular luster results from a neural conflict between ON and OFF visual pathways at an early binocular level. Support for this idea was found in a previous study in which the empirical luster judgments strongly correlated with the predictions of an interocular conflict model which was based on such ON–OFF pairings. However, our original model could not account for the fact that weaker lustrous sensations can also be evoked by stimuli showing contrast polarities of same sign between eyes. In the present study we present an improved model that also includes ON–ON and OFF–OFF pairings. The predictive power of this model was tested in a series of four experiments, using a total of about 500 different center–ring–surround configurations as test stimuli. We found that, overall, our modified version accounts for more than 80% of the variance in the empirical luster judgments and that the former problems could be largely resolved. Our results further suggest a nonlinear transducer function for the binocular conflict signals.

Visual attention in change blindness for objects and shadows

Studies have found that observers pay less attention to cast shadows in images than to better illuminated regions. In line with such observations, a recent study has suggested stronger change blindness for shadows than for objects (Ehinger et al., 2016). We here examine the role of (overt) visual attention in these findings by recording participants' eye movements. Participants first viewed all original images (without changes). They then performed a change detection task on a subset of the images with changes in objects or shadows. During both tasks, their eye movements were recorded. In line with the original study, objects (subject to change in the change detection task) were fixated more often than shadows. In contrast to the previous study, better change detection was found for shadows than for objects. The improved change detection for shadows may be explained by the balancing of trials with object and shadow changes in the present study. Eye movements during change detection indicated that participants searched the bottom half of the images. Shadows were more often present in this region, which may explain why they were easier to find.

The application of the spot the difference teaching method in clinical skills training for residents

BACKGROUND

Clinical skill training (CST) is indispensable for first-year surgical residents. It can usually be carried out through video-based flipped learning (FL) within a web-based learning environment. However, we found that residents lack the process of reflection, blindly imitating results in losing interest and passion for learning in the traditional teaching pattern. The teaching method of "spot the difference" (SDTM), which is based on the fundamentals of the popular game of "spot the difference," is designed to improve students' participation and reflective learning during skill training. This study aimed to evaluate this novel educational model's short-term and long-term effectiveness for surgical residents in China.

METHODS

First-year residents who required a three-month rotation in the head and neck surgery department were recruited to participate in a series of CSTs. They were randomized into SDTM and traditional FL (control) groups. Clinical skill performance was assessed with validated clinical skill scoring criteria. Evaluations were conducted by comparing the scores that contain departmental rotation skill examinations and the first China medical licensing examination (CMLE) performance on practical skills. In addition, two-way subjective evaluations were also implemented as a reference for the training results. Training effects were assessed using t tests, Mann-Whitney-Wilcoxon tests, chi-square tests, and Cohen' s effect size (d). The Cohen' s d value was considered to be small (<0.2), medium (0.2-0.8), or large (>0.8).

RESULTS

The SDTM group was significantly superior to the control group in terms of after-department skill examination (t=2.179, p<0.05, d=0.5), taking medical history (t=2.665, p<0.05, d=0.59), and CMLE performance on practical skill (t=2.103, p<0.05, d=0.47). The SDTM members rated the curriculum more highly than the control on the items relating to interestingness and participation (p < 0.05) with large effect sizes (d >0.8). There were no significant differences between the two groups on clinical competence (t=0.819, p=0.415, d=0.18), the first-time pass rate for CMLE (χ2 =1.663, p=0.197, d=0.29), and short-term operational skills improvement (t=1.747, p=0.084, d=0.39).

CONCLUSIONS

SDTM may be an effective method for enhancing residents' clinical skills, and the effect is significant both short- and long-term. The improvement effect seemed to be more significant in the peer-involved SDTM than training alone. However, despite positive objective results, SDTM still risks student learning burnout.

TRIAL REGISTRATION

ISRCTN registry, ISRCTN10598469 , 02/04/2022，retrospectively registered.

Binocular luster - A review

Binocular luster is a visual phenomenon that can be elicited by dichoptic stimuli showing an interocular difference in color or luminance contrast. For instance, when the two eyes are presented with simple center-surround stimuli in which the center patch in one eye is brighter and in the other eye darker than the common surround, the center patch in the fused percept assumes a lustrous appearance reminiscent of metal or graphite. Soon after the discovery of this phenomenon in the mid-19th century, it was intensively studied and several explanations were proposed. After this initial phase, however, research interest waned significantly. Stimulated by new insights into related phenomena and the underlying physiological mechanisms, the last 20 years have seen an increase in research activity in this field, which has considerably expanded our understanding of binocular luster. In this paper, we provide a detailed review of research on binocular luster over the past 170 years. We present and discuss the existing findings in a number of separate sections, dealing with 1) the phenomenology of binocular luster, 2) different theories that have been proposed, 3) several factors influencing the lustrous impression, 4) the relationship between binocular luster and binocular rivalry, 5) the current understanding of its neural basis, and 6) potential applications based on binocular luster.