Q: Why do different people see the spinning dancer moving in different directions?
A: Because the stimulus is ambiguous (bistable) and has no depth cues. The brain relies on top-down processing and individual neural differences, causing some people to perceive clockwise motion and others to perceive counter-clockwise motion.
Q: Why can the viewer see the spinning dancer reverse direction?
A: Both motion directions are equally plausible to the visual system. Neurons responsible for each directional interpretation compete, and the brain switches between them because neither interpretation is definitively correct.
Q: Why does prolonged viewing of the spinning dancer cause a motion aftereffect?
A: Motion-specific neurons adapt and reduce firing after prolonged exposure. Neurons for the opposite direction remain more active, causing the perceived motion to flip.
Q: What did George Wald discover about visual transduction?
A: Wald discovered that Vitamin A (retinal) is a key component of rhodopsin in rods and that light splits rhodopsin into opsin and retinal, initiating phototransduction.
Q: How does George Wald’s work relate to dark adaptation?
A: Wald described the visual cycle, showing how retinal is regenerated after bleaching. This explains how sensitivity recovers in the dark after exposure to bright light.
Q: How did George Wald contribute to our understanding of color vision?
A: Using spectral measurements of cone pigments, Wald supported trichromatic theory by showing that three cone types have different wavelength sensitivities.
Q: What did Keffer Hartline study and discover?
A: Hartline recorded optic nerve responses in simple eyes (e.g., horseshoe crab) and demonstrated how light is converted into neural activity.
Q: What is lateral inhibition, according to Hartline?
A: Lateral inhibition occurs when a strongly activated photoreceptor suppresses the activity of neighboring receptors. This enhances contrast and helps with edge detection.
Q: How does Hartline’s work relate to receptive fields?
A: Lateral inhibition explains center-surround receptive fields in retinal ganglion cells, a key mechanism in early visual processing.
Q: How do Wald’s and Hartline’s discoveries connect?
A: Wald explained the chemical conversion of light into neural signals, while Hartline explained how retinal circuits refine these signals through lateral inhibition before sending them to the brain.
