Klein Lab

University of California, Berkeley | Vision Science Program

Examples of Ongoing Research

 

Cortical retinotopy and specificity of perceptual learning revealed by EEG
In our daily lives our brains are constantly adapting to new visual experiences and learning optimal solutions to new tasks. Understanding the mechanisms of neural plasticity is crucial to develop sound training paradigms. One important step is to identify cortical sites that participate in learning new tasks and their relative dynamics. Functional magnetic resonance imaging (fMRI) gives insight to the sites of perceptual learning but technologies like electroencephalography (EEG) are needed to reveal the dynamic interplay between cortical areas that change with learning. This project has two broad goals: 1) to develop methods for using EEG for isolating the event related activity in closely spaced regions of human cortex in response to visual stimulation. The challenge is that when the sources of brain waves are spatially close together, it has so far been an intractable problem to isolate the activity to individual brain areas. And: 2) to use these new methods to identify the locations and temporal dynamics of changes produced by perceptual learning of challenging visual tasks.

 

For details and abstract see: National Science Foundation (NSF)

 

Processes and mechanisms of perceptual learning in normal and compromised vision
The broad aim of our this project is to gain a deeper understanding of the mechanisms of perceptual learning (PL) in normal and compromised visual systems that could potentially benefit from effective perceptual learning paradigms. Using advanced psychophysical methods, we aim to identify the mechanisms underlying the losses and to what extent perceptual learning can ameliorate these losses. In addition, by identifying the underlying mechanisms of PL we anticipate being able to explain the large individual differences commonly found in PL studies.

 

For details and abstract see: National Eye Institute (NEI)

 

Single cone psychophysics

 

Imagine a technology able to noninvasively identify individual cones in the living human retina and selectively stimulate them to study their contribution to visual perception. This technology could also track retinal functional organization at the border of a visual scotoma to study mechanisms disease and outcomes of treatment regimes. The technology does not yet exist but the current generation of the adaptive optics scanning laser ophthalmoscope (AOSLO), with its unique ability to compensate for retinal motion and image the cone mosaic, comes very close. The remaining obstacle is real time correction of transverse chromatic aberration (TCA) between the infrared beam and a visible light laser beam so that we can repeatedly, continuously and reliably image and stimulate the individual identified cones from day to day. Achieving and validating this capability is the principal goal (Aim 1) of this proposal. The validation of TCA error correction includes both physical (image processing) and innovative perceptual (chromatic shifts) techniques of characterizing the accuracy and reliability of stimulating the center of single cones. The method includes rapid identification of L & M cone classes which is itself a significant advance. In Aim 2, after we map out an array of cones identified by class near the fovea, we will stimulate different single L and M cones within the array while observers judge the intensity, hue and saturation of the flash. This single cone stimulation aim focuses on characterizing the stability of percepts within a cone and consistency across cones of the same class. This step will establish the parameters of cone activation and resultant percepts and clarify any constraints it might impose on future research. Along the way we expect to confirm or discredit hypotheses on the consequences of different cone class neighborhoods around the single probed cone. In Aim 3 we examine mechanisms of light adaptation; does it occur within a single cone? With our superior image stabilization, small steady, intense pedestals delivered to the center of a cone are expected to result in rapid Troxler fading. Once faded, the pedestal may not saturate the incremental test response (as in the Westheimer effect) but instead act largely like a uniform field with a constant cone-selective Weber law behavior. What appeared to be cone saturation may result from eye tremor. The proposed single cone studies will demonstrate the capabilities of the AOSLO. Future studies involving simultaneous and independent stimulation of multiple identified cones will be just as easy to perform and be able to address research questions extending from color to spatial vision in general. A number of specific projects are under way.

 

For details and abstract see: National Eye Institute (NEI)

head surface plot showing occipital activity

 

dartboard stimulus1

 

Click to participate in one of our studies

 

Principal Investigator:

Stanley A. Klein, Ph.D.

Professor of Vision Science

360 Minor Hall #2020

School of Optometry

UC Berkeley, 94720-2020

sklein@berkeley.edu