{"id":370,"date":"2023-03-02T20:16:20","date_gmt":"2023-03-02T20:16:20","guid":{"rendered":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/chapter\/4-1-3-learn-it-testing-blindsight\/"},"modified":"2023-08-04T17:25:14","modified_gmt":"2023-08-04T17:25:14","slug":"4-1-3-learn-it-testing-blindsight","status":"publish","type":"chapter","link":"https:\/\/content.one.lumenlearning.com\/introductiontopsychology\/chapter\/4-1-3-learn-it-testing-blindsight\/","title":{"raw":"Consciousness: Learn It 3\u2014Testing Blindsight","rendered":"Consciousness: Learn It 3\u2014Testing Blindsight"},"content":{"raw":"

How Can Blindsight Happen?<\/h2>\r\nYour conscious experience of the world around you, of the choices and decisions you make, and of the emotions and attitudes that motivate you are not the totality of your mental activity or of your brain\u2019s processing of information. Many, perhaps most, psychologists believe that consciousness is only a small part of your total cognitive activity.[footnote]Source: http:\/\/marketingland.com\/wp-content\/ml-loads\/2014\/09\/iceberg-ss-1920.jpg[\/footnote]\r\n\r\nA person is considered to be blind if they have no conscious experience of the visual world. This conscious experience is based on the flow of information from the eyes through the thalamus in the middle of the brain to the primary visual cortex in the occipital lobe at the back of the brain. If the primary visual cortex is damaged or fails to receive input due to the disruption of visual\u00a0pathways, then the person will not \u201csee\u201d the objects and events that we normally associate with vision. Remarkably, some people who are blind can still respond to visual stimuli\u2014a phenomena known as blindsight<\/strong>.\r\n\r\n[caption id=\"attachment_4713\" align=\"alignright\" width=\"464\"]\"Overhead<\/a> Figure 1.<\/strong>\u00a0The green and purple lines represent the primary visual pathway that produces our conscious experience of vision. The red lines roughly represent the secondary pathways that produce visual information with reduced conscious experience, or none at all. (These secondary pathways are not shown precisely).[\/caption]\r\n\r\nBlindsight occurs because the visual system has a primary pathway (retina to thalamus to primary visual cortex), but it also<\/em> has secondary pathways (retina to thalamus to other brain areas). These \u201cother brain areas\u201d include parts of the frontal lobe that guide eye movements, parts of the midbrain that help guide visual attention, and parts of the occipital lobe that process features of visual perception, including shape, movement, and color.[footnote]A recent literature review of evidence for the existence of the pathways to the cerebral cortex: Rabbo, F. A., Koch, G., Lefevre, C., & Seizeur, R. (2015). Direct geniculo-extrastriate pathways: A review of the literature. Surgical and Radiologic Anatomy, 37(8), 891-899.[\/footnote]\r\n\r\nThe existence of visual processing areas for isolated features of vision and the fact that these areas get some direct visual information (i.e, input that does not first go to the primary visual cortex) means that it is possible for a person to respond accurately to questions about color or motion or shape without consciously \u201cseeing\u201d the objects that have color or shape or are moving.\r\n\r\n
[ohm2_question height=\"400\"]3962[\/ohm2_question]<\/section>It is important to remember that everyone has these same \u201cunconscious\u201d pathways in their visual system, not just those with visual impairments. That means your conscious experience of the visual world may not include all of the visual information you are processing. In other words, you may \u201cknow\u201d more than you \u201csee.\u201d\r\n\r\nBlindsight is not the only condition that involves unconscious or low-consciousness processing. Other neurological syndromes that have an unconscious element include amnesia, hemispatial neglect, dyslexia, aphasia, and various agnosias.[footnote]See Consciousness Lost and Found: A Neuropsychological Exploration by Larry Weiskrantz (1997, Oxford University Press). Dr. Weiskrantz is one of the scientists who first described blindsight and studied people with the condition.[\/footnote]\r\n\r\n
\r\n

Creating Blindsight in the Laboratory<\/h3>\r\nWouldn\u2019t it be great if we could produce blindsight in the laboratory, in order to better understand visual processing and conscious experience?\r\n\r\nIt turns out, researchers have already done it. Using precisely aimed magnetic pulses, researchers can temporarily disrupt specific areas of the primary visual cortex\u2014the area responsible for conscious vision\u2014without injury. This \u201cblindness\u201d lasts only a fraction of a second, after which vision returns to normal.\u00a0Would you volunteer to be a participant?\r\n\r\nLet\u2019s look at how this works.\r\n

TMS: Transcranial Magnetic Stimulation<\/strong><\/h4>\r\nTranscranial magnetic stimulation (TMS) is a procedure used to stimulate neurons in the brain. A device referred to as a \u201cwand\u201d contains an electric coil that generates a magnetic field that in turn creates a small electric current in the brain.[footnote]The physics of electromagnetism is fascinating, but we will spare you the details here. You may have studied it in some other class, and there are many readable online sources (e.g., Wikipedia). TMS is a great example of the convergence of technology and psychology that is the basis of modern neuroscience.[\/footnote] The electric current induces neurons (brain cells) to produce neural signals called action potentials. When action potentials are produced in normal brain processes, they allow neurons to communicate with one another. However, when action potentials are induced by an outside force\u2014here by the TMS wand\u2014they are meaningless and temporarily interfere with normal communication between neurons. If only a single pulse of electromagnetic energy is produced, then the disruption of the neurons in the targeted region lasts only a fraction of a second. Multiple pulses, called repetitive TMS (rTMS), can produce longer-lasting effects. In fact, rTMS is now used by therapists as a treatment for depression and neuropathic pain.\r\n\r\nThe TMS pulse can be aimed very precisely at a small area of the brain. When the target is the primary visual cortex in the occipital lobe, the TMS pulse can be focused to interfere with neural communication in a tiny region of the visual field\u2014occurring for such a short time\u00a0and in such a small area that you would not even notice. But however\u00a0brief the duration or tiny the affected area, the person receiving the TMS pulse is temporarily blind in a small part of the visual field.\r\n

Conclusions from the Research<\/h3>\r\nExperimenters have succeeded in producing the experience of blindness using the TMS apparatus, and they\u00a0have also succeeded in producing evidence for the unconscious processing of features of the visual experience in normal (college student) volunteers. These results, when put together with the experiences of people with neurological damage, strengthen the case for the theory that some of our visual perception of the world takes place outside of our awareness.\u00a0Researchers and their volunteer participants helped show that this unconscious processing is not the result of brain damage, but\u00a0is instead part of our normal perception of the world.\r\n\r\n<\/section>\r\n

Some Final Thoughts<\/h2>\r\nThis module is about consciousness. It is common to assume that everything we know about the world around us and about our own thoughts and internal experiences must go through the doorway of our conscious mind. Evidence from blindsight is\u00a0one of several lines of research that shows\u00a0we process more information than we are consciously aware of. Learning just how much this unconscious information can influence our thoughts, actions,\u00a0preferences, and beliefs, is an important challenge for the next\u00a0generation of rising scientists.","rendered":"

How Can Blindsight Happen?<\/h2>\n

Your conscious experience of the world around you, of the choices and decisions you make, and of the emotions and attitudes that motivate you are not the totality of your mental activity or of your brain\u2019s processing of information. Many, perhaps most, psychologists believe that consciousness is only a small part of your total cognitive activity.[1]<\/sup><\/a><\/p>\n

A person is considered to be blind if they have no conscious experience of the visual world. This conscious experience is based on the flow of information from the eyes through the thalamus in the middle of the brain to the primary visual cortex in the occipital lobe at the back of the brain. If the primary visual cortex is damaged or fails to receive input due to the disruption of visual\u00a0pathways, then the person will not \u201csee\u201d the objects and events that we normally associate with vision. Remarkably, some people who are blind can still respond to visual stimuli\u2014a phenomena known as blindsight<\/strong>.<\/p>\n

\"Overhead<\/a>
Figure 1.<\/strong>\u00a0The green and purple lines represent the primary visual pathway that produces our conscious experience of vision. The red lines roughly represent the secondary pathways that produce visual information with reduced conscious experience, or none at all. (These secondary pathways are not shown precisely).<\/figcaption><\/figure>\n

Blindsight occurs because the visual system has a primary pathway (retina to thalamus to primary visual cortex), but it also<\/em> has secondary pathways (retina to thalamus to other brain areas). These \u201cother brain areas\u201d include parts of the frontal lobe that guide eye movements, parts of the midbrain that help guide visual attention, and parts of the occipital lobe that process features of visual perception, including shape, movement, and color.[2]<\/sup><\/a><\/p>\n

The existence of visual processing areas for isolated features of vision and the fact that these areas get some direct visual information (i.e, input that does not first go to the primary visual cortex) means that it is possible for a person to respond accurately to questions about color or motion or shape without consciously \u201cseeing\u201d the objects that have color or shape or are moving.<\/p>\n