Perception Lecture 6

  • Photoreceptor: Specialized cells in the retina (rods and cones) that convert light into electrical signals.

  • Inner Segment: The part of a photoreceptor that contains the cell nucleus and synaptic terminals.

  • Outer Segment: The part of a photoreceptor containing photopigments.

  • Photopigment: A light-sensitive molecule in photoreceptors composed of opsin and a chromophore.

  • Opsin: A protein component of photopigments that determines the wavelength sensitivity of the photoreceptor.

  • Chromophore: The light-absorbing molecule within photopigments; in mammals, this is 11-cis retinal.

  • Phototransduction: The process by which photoreceptor cells convert light into electrical signals.

  • Photoisomerization: The process by which 11-cis retinal changes to all-trans retinal upon exposure to light.

  • Photopigment Regeneration: The process of converting all-trans retinal back to 11-cis retinal.

  • Rods: Photoreceptors specialized for low-light (scotopic) vision; highly sensitive to light, but do not convey colour information.

  • Cones: Photoreceptors specialized for bright light (photopic) vision, and are responsible for colour vision.

  • Rhodopsin: The photopigment found in rods.

  • Photopsin: The photopigment found in cones.

  • S-Cones: Cones sensitive to short wavelengths, associated with blue perception.

  • M-Cones: Cones sensitive to medium wavelengths, associated with green perception.

  • L-Cones: Cones sensitive to long wavelengths, associated with red perception.

  • Melanopsin: Photopigment found in some photoreceptors that monitor ambient light and influence circadian rhythm.

  • Duplex Retina: Refers to the dual functionality of the retina with both rods (for scotopic vision) and cones (for photopic vision).

  • Photopic Vision: Vision under well-lit conditions, primarily mediated by cones.

  • Scotopic Vision: Vision in low-light conditions, primarily mediated by rods.

  • Dark Adaptation: The process by which the eyes adjust to low-light conditions.

  • Lateral Inhibition: A neural mechanism where active neurons suppress neighbouring neurons.

  • Receptive Field: The region on the retina in which stimuli influence a neuron’s firing rate.

  • ON-center/OFF-surround Cells: Ganglion cells activated by light in the centre and inhibited by light in the surround.

  • OFF-center/ON-surround Cells: Ganglion cells activated by light in the surround and inhibited by light in the centre.

  • Bipolar Cells: Retinal interneurons that connect photoreceptors to ganglion cells.

  • Graded Potentials: Continuous variations in the amplitude of a postsynaptic potential.

  • Ganglion Cells: Retinal neurons that send signals from the retina to the brain via the optic nerve.

  • Visual Acuity: The smallest spatial detail that can be resolved.

  • Visual Angle: The size of a visual stimulus on the retina.

  • Grating: A pattern of alternating black and white stripes used to measure visual acuity.

  • Spatial Frequency: The number of cycles of a pattern within one degree of visual angle.

  • Convergence: The number of photoreceptors that synapse onto a single bipolar cell.

  • Fovea: The central region of the retina, specialised for high acuity.

  • Optic Chiasm: The site where half of the optic nerve fibers from each eye decussate to the contralateral brain hemisphere.

  • Temporal Retina: The part of the retina that receives light from the contralateral visual field, and does not decussate in the optic chiasm.

  • Nasal Retina: The part of the retina that receives light from the ipsilateral visual field, and decussates in the optic chiasm.

  • Optic Tract: Retinal projections beyond the optic chiasm.

  • Lateral Geniculate Nucleus (LGN): A nucleus in the thalamus where most optic tract fibers synapse.

  • Magnocellular Layers: Layers 1 and 2 of the LGN that process peripheral vision and are input from parasol retinal ganglion cells.

  • Parvocellular Layers: Layers 3-6 of the LGN that process central vision and are input from midget retinal ganglion cells.

  • Koniocellular Layers: Located in intralaminar regions of the LGN, specialized for colour perception.

  • Superior Colliculus (SC): A midbrain structure that receives direct input from the retina, involved in visual reflexes and unconscious visual processing.

  • Blindsight: Unconscious visual perception in patients with damage to the primary visual cortex.

  • Optic Radiations: Axons from the LGN that project to the primary visual cortex (V1).

  • Primary Visual Cortex (V1): The first area of the cortex to process visual information.

  • Retinotopic Mapping: The mapping of the visual field onto the retina and then onto visual areas of the brain.

  • Magnocellular Pathway: A visual pathway that projects to the parietal cortex and is specialized for processing motion.

  • Parvocellular Pathway: A visual pathway that projects to the temporal cortex and is specialized for object recognition.

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