Associations Between Binocular Depth Perception and Performance Gains in Laparoscopic Skill Acquisition

The ability to perceive differences in depth is important in many daily life situations. It is also of relevance in laparoscopic surgical procedures that require the extrapolation of three-dimensional visual information from two-dimensional planar images. Besides visual-motor coordination, laparoscopic skills and binocular depth perception are demanding visual tasks for which learning is important. This study explored potential relations between binocular depth perception and individual variations in performance gains during laparoscopic skill acquisition in medical students naïve of such procedures. Individual differences in perceptual learning of binocular depth discrimination when performing a random dot stereogram (RDS) task were measured as variations in the slope changes of the logistic disparity psychometric curves from the first to the last blocks of the experiment. The results showed that not only did the individuals differ in their depth discrimination; the extent with which this performance changed across blocks also differed substantially between individuals. Of note, individual differences in perceptual learning of depth discrimination are associated with performance gains from laparoscopic skill training, both with respect to movement speed and an efficiency score that considered both speed and precision. These results indicate that learning-related benefits for enhancing demanding visual processes are, in part, shared between these two tasks. Future studies that include a broader selection of task-varying monocular and binocular cues as well as visual-motor coordination are needed to further investigate potential mechanistic relations between depth perceptual learning and laparoscopic skill acquisition. A deeper understanding of these mechanisms would be important for applied research that aims at designing behavioral interventions for enhancing technology-assisted laparoscopic skills.

Modulation depth discrimination by cochlear implant users

Cochlear implants (CIs) convey the amplitude envelope of speech by modulating high-rate pulse-trains. However, not all of the envelope may be necessary to perceive amplitude modulations (AM); the effective envelope depth may be limited by forward and backward masking from the envelope peaks. Three experiments used modulated pulse-trains to measure which portions of the envelope can be effectively processed by CI users as a function of AM frequency. Experiment 1 used a three-interval forced-choice task to test the ability of CI users to discriminate less-modulated pulse trains from a fully-modulated standard, without controlling for loudness. The stimuli in Experiment 2 were identical, but a two-interval task was used in which participants were required to choose the less-modulated interval, ignoring loudness. Catch trials, in which judgements based on level or modulation depth would give opposing answers were included. Experiment 3 employed novel stimuli whose modulation envelope could be modified below a variable point in the dynamic range, without changing the loudness of the stimulus. Overall, results showed that substantial portions of the envelope are not accurately encoded by CI users. Experiment 1, where loudness cues were available, participants on average were insensitive to changes in the bottom 30% of their dynamic range. In Experiment 2, where loudness was controlled, participants appeared insensitive to changes in the bottom 50% of the dynamic range. In Experiment 3, participants were insensitive to changes in the bottom 80% of the dynamic range. We discuss potential reasons for this insensitivity and implications for CI speech-processing strategies.

Correlated structure of neuronal firing in macaque visual cortex limits information for binocular depth discrimination

Variability in cortical neural activity potentially limits sensory discriminations. Theoretical work shows that information required to discriminate two similar stimuli is limited by the correlation structure of cortical variability. We investigated these information-limiting correlations by recording simultaneously from visual cortical areas V1 and V4 in macaque monkeys, performing a binocular, stereo-depth discrimination task. Within both areas, noise correlations on a rapid temporal scale (20-30ms) were stronger for neuron-pairs with similar selectivity for binocular depth, meaning that these correlations potentially limit information for making the discrimination. Between-area correlations (V1 to V4) were different, being weaker for neuron pairs with similar tuning, and having a slower temporal scale (100+ms). Fluctuations in these information-limiting correlations just prior to the detection event were associated with changes in behavioral accuracy. Although these correlations limit the recovery of information about sensory targets, their impact may be curtailed by integrative processing of signals across multiple brain areas.

Confocal Scanning Laser Microscopy in Medicine

Confocal Scanning Laser Microscopy (CSLM) offers high resolution morphological details and generates en-face images with excellent depth discrimination for visualizing different structures of the living human body non-invasively. There have been significant advances in technology since the CSLM was first defined. It has been used commonly, especially in ophthalmological area, in order to diagnose and give direction for the treatment of corneal pathologies. Ocular surface, corneal subbasal nerve plexus, filtering blebs of glaucoma surgery were also investigated widely by CSLM. With the improvements in CSLM technology over time, it is widely used in other fields than ophthalmology. The combined use of CSLM with the slit lamp biomicroscopy and optical coherence tomography will also lead to significant advances in the diagnosis and treatment of more diseases in the future.