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01:22Photoreceptors and Visual Pathways
At the molecular level, visual signals trigger transformations in photopigment molecules, resulting in changes in the photoreceptor cell's membrane potential. The photon's energy level is denoted by its wavelength, with each specific wavelength of visible light associated with a distinct color. The spectral range of visible light, classified as electromagnetic radiation, spans from 380 to 720 nm. Electromagnetic radiation wavelengths exceeding 720 nm fall under the infrared category, whereas...
01:16Focusing of Light in the Eye
Light rays enter the eye through the cornea, a transparent dome-shaped tissue that is the eye's outermost layer. The cornea bends or refracts, light rays traveling to the pupil. The shape of the cornea determines how much of the light is bent and whether the image will be focused correctly on the retina at the back of the eye. Once the light has passed through both refraction layers, it converges into a single focal point onto a small area. This is where photoreceptors start transforming...
01:11Blinding
Blinding is a commonly used method of not telling participants which treatment a subject is receiving. Blinding is a critical part of a randomized control trial or RCT. It reduces the bias that affects the results. In an RCT, blinding is used in the form of a placebo. A placebo effect occurs when untreated subjects falsely believe they have received the treatment and report improved symptoms. A placebo or a dummy treatment is administered to subjects to negate the bias caused by such an effect.
01:24Vision
Vision is the result of light being detected and transduced into neural signals by the retina of the eye. This information is then further analyzed and interpreted by the brain. First, light enters the front of the eye and is focused by the cornea and lens onto the retina—a thin sheet of neural tissue lining the back of the eye. Because of refraction through the convex lens of the eye, images are projected onto the retina upside-down and reversed.
00:50Unrenewable Cells
In humans, the photoreceptor cells of the eye and sensory hair cells of the ear lack stem cells. These cells are thus unrenewable and cannot be replaced when they are damaged or destroyed.
Photoreceptors
The retina is composed of several layers and contains specialized cells called photoreceptors. The photoreceptors (rods and cones) change their membrane potential when stimulated by light energy. There are two types of photoreceptors—rods and cones—which differ in the shape of their outer...
Photoreceptors
The retina is composed of several layers and contains specialized cells called photoreceptors. The photoreceptors (rods and cones) change their membrane potential when stimulated by light energy. There are two types of photoreceptors—rods and cones—which differ in the shape of their outer...
02:07Blind Procedures
Ideally, the people who observe and record the children’s behavior are unaware of who was assigned to the experimental or control group, in order to control for experimenter bias. Experimenter bias refers to the possibility that a researcher’s expectations might skew the results of the study. Remember, conducting an experiment requires a lot of planning, and the people involved in the research project have a vested interest in supporting their hypotheses. If the observers knew which child was...
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Related Experiment Video
Updated: Jul 5, 2026
07:12
A Gaze-Contingent Display Framework for Perceptual Learning Research with Simulated Central Vision Loss
Published on: April 11, 2025
Is blindsight just degraded normal vision?
1Department of Experimental Psychology, Oxford University, South Parks Road, Oxford, OX1 3UD, UK. larry.weiskrantz@psy.ox.ac.uk
Experimental Brain Research
|April 29, 2008
Summary
Blindsight, or vision without awareness, is not simply degraded normal vision. Its unique characteristics suggest qualitative differences from standard visual processing, even when degraded.
Area of Science:
- Neuroscience
- Cognitive Science
- Psychology
Background:
- Blindsight is characterized by preserved visual abilities despite the absence of conscious visual experience.
- It has been traditionally viewed as a degraded form of normal vision due to weakened visual parameters.
Purpose of the Study:
- To investigate whether blindsight performance is uniformly degraded compared to normal vision.
- To explore the qualitative similarities and differences between blindsight and degraded normal vision.
Main Methods:
- Analysis of blindsight performance across various visual parameters.
- Comparison of blindsight capabilities with normal vision under degraded conditions (e.g., reduced contrast, noise).
- Examination of specific phenomena in blindsight, such as selective color loss and 'prime-sight'.
Main Results:
- Blindsight performance is not uniformly degraded; excellent performance can occur within specific visual parameter ranges.
- Blindsight vision exhibits qualitative differences from degraded normal vision, including selective deficits (e.g., color vs. luminance) and super-sensitivity.
- Stimulus contrast reduction does not always parallel the degradation of blindsight performance.
Conclusions:
- Blindsight represents a distinct mode of visual processing, not merely a weakened version of normal vision.
- The qualitative differences challenge conservative explanations and highlight the complexity of visual awareness and processing.
- Further neural and philosophical analysis is needed to understand the mechanisms underlying blindsight.