H7 the Seeing Brain

• Sensation


  The effects of a stimulus on the sensory organs
• Perception


  The elaboration and interpretation of a sensory stimulus based on knowledge of how objects are structured
• Retina


  The internal surface of the eyes that consists of multiple layers. Some layers contain photoreceptors that convert light to neural signals, and others consist of neurons themselves
• Photoreceptors


  • Rod cells
  • Cone cells
• Rod cells

  A type of photoreceptor specialized for low levels of light intensity, such as those found at night
• Cone cells


  A type of photoreceptor specialized for high levels of light intensity, such as those found during the day, and specialized for the detection of different wavelengths (color)
• Fovea


  The highest concentration of cones is at a point called the fovea, and the level of detail that can be perceived (or visual acuity) is greatest at this point
• Receptive Field


  The region of a space that elicits a response form a given neuron
• Blind spot


  The point at which the optic nerve leaves the eye. There are no rods and cones present there
• Primary visual cortex (or V1)


  The first stage of visual processing in the cortex; the region retains the spatial relationships found on the retina and combines simple visual features into more complex ones
• Layers of LGN

  • Parvocellular layers
  • Magnocellular layers
• Parvocellular layers


  Upper 4 layer, small cell bodies, respond to detail and color vision
• Magnocellular layers


  Lower 2 layer, big cell bodies, more sensitive to movement than color, respond to larger areas of visual field
• Konio cell or K


  In LGN lies between M and P layers, show less functional specificity then M and P cells, have a different pattern of connectivity
• Simple cells


  Simple cells respond to different orientations, but also respond to points of light, in V1
• Complex cells


  Orientation selective too, distinguish from simple cells by larger receptive fields and require stimulation on their entire length, respond to light in a particular orientation, combine the responses of several simple cells
• Hypercomplex cells


  Outside of V1, combine the responses of several complex cells, unlike complex cells, they are sensitive to length as well as orientation
• Cortical blindness


  Damage to the visual areas in the brain (V1). Despite having healthy eyes and optic nerves, individuals with cortical blindness are unable to process visual information
• Hemianopia


  Cortical blindness restricted to one half of the visual field (associated with damage to the primary visual cortex in one hemisphere)
• Quadrantanopia

  Cortical blindness restricted to a quarter of the visual field
• Scotoma


  A small region of cortical blindness
• Retinotopic organization


  The receptive fields of a set of neurons are organized in such a way as to reflect the spatial organization present in the retina
• Blindsight


  A symptom in which the patient reports not being able to consciously see stimuli in a particular region but can nevertheless perform visual discriminations (e.g., long, short) accurately
• Ventral stream


  In vision, a pathway extending from the occipital lobes to the temporal lobes involved in object recognition, memory and semantics
• Dorsal stream


  In vision, a pathway extending from the occipital lobes to the parietal lobes involved in visually guided action and attention
• V4

  Associated with color perception
• Achromatopsia


  A failure to perceive color (the world appears in grayscale), not to be confused with color blindness (deficient or absent types of cone cell)
• Color constancy


  The color of a surface is perceived as constant even when illuminated in different lighting conditions
• V5/MT

  Associated with motion perception
• Biological motion


  The ability to detect whether a stimulus is animate or not from movement cues alone
• Akinetopsia


  A failure to perceive visual motion
• Structural descriptions

  A memory representation of the three-dimensional structure of objects
• Apperceptive agnosia


  A failure to understand the meaning of objects due to a deficit at the level of object perception
• Associative agnosia


  A failure to understand the meaning of objects due to a deficit at the level of semantic memory
• Gestalt principles


  • The law of proximity
  • The law of similarity
  • The law of good continuation
  • The law of closure
  • The law of common fate