6.5

• On-center cells respond to lights shone in the central region of their receptive fields with “on” firing and to lights shone in the periphery of their receptive fields with inhibition, followed by “off” firing when the light is turned off.
• Off-center cells respond with inhibition and “off” firing in response to lights in the center of their receptive fields and with “on” firing to lights in the periphery of their receptive fields.
• The receptive fields of most primary visual cortex neurons fall into one of two classes:

  simple or complex.
• Simple cells were similar to lower layer IV neurons in a way that:

  • it had have receptive fields that can be divided into antagonistic “on” and “off” regions and are thus unresponsive to diffuse light.
  • monocular
• Hubel and Wiesel (1979) began their studies of visual system neurons by recording from the three levels of the retina-geniculate-striate system:

  1. retinal ganglion cells
  2. lateral geniculate neurons
  3. striate neurons of lower layer IV
• Simple cells were different to lower layer IV neurons:

  1. receptive fields of simple cells are straight lines rather than circles.
  2. responds maximally only when its preferred straight-edge stimulus is in a particular position and in a particular orientation
  3. receptive fields of simple cortical cells are rectangular rather than circular.
• Like simple cells, complex cells have:

  1. rectangular receptive fields
  2. respond best to straight-line stimuli in a specific orientation
  3. unresponsive to diffuse light
• Complex cells differ from simple cells:

  1. larger receptive fields
  2. it is not possible to divide the receptive fields of complex cells into static “on” and “off” regions.
  3. Binocular
• A complex cell responds to a particular straight-edge stimulus of a particular orientation regardless of its position within the receptive field of that cell.
• What you learn about the cell by stimulating one eye is confirmed by stimulating the other. What is more, if the appropriate stimulation is applied through both eyes simultaneously, a binocular cell usually fires more robustly than if only one eye is stimulated.

  Binocular Complex Striate Cells
• True or False, studies of the responses of visual cortex to natural scenes indicate that the response of a visual cortex neuron depends only on the stimuli in its receptive field.

  False, depends not only on the stimuli in its receptive field but also on the larger scene in which these stimuli are embedded.
• The influences on a visual neuron’s activity that are caused by stimuli outside the neuron’s receptive field are generally referred to as contextual influences.
• Black is experienced when there is an absence of light
• The perception of white is produced by an intense mixture of a wide range of wavelengths in roughly equal proportions.
• Perception of gray is produced by the same mixture at lower intensities.
• True or False, the perception of an object’s color depends on the wavelengths of light that it reflects into the eye.

  True
• Component Theory (Trichromatic Theory) was pioneered by?

  Thomas Young 1802
• Component Theory (Trichromatic Theory) was revised by:

  Hermann von Helmholtz in 1852
• This states that there are three different kinds of color receptors (cones), each with a different spectral sensitivity, and the color of a particular stimulus is presumed to be encoded by the ratio of activity in the three kinds of receptors.

  Component Theory (Trichromatic Theory)
• Opponent-Process Theory was pioneered by?

  Ewald Hering in 1878