HOMEWORK #2:

Checklist:
  (a) due Wednesday 11/15/00 (12 days), under my door (CSB 171)
  (b) use this page as the first page
  (c) staple all pages together
  (d) one page maximum per answer (less than a page is better!)
  (e) each answer on a separate page
  (f) figures on same page as answer
  (g) word-processor text with hand-drawn figures preferred

1. (a) The main streams of information at the level of the dLGN appear to be left versus right eye, and sustained X-like versus transient Y-like versus intralaminar, on the other. Briefly summarize the current view of the main streams of visual information at the level of V1. (b) Illustrate the left visual hemifield and then the orientation of the retinotopic map in right hemisphere V1, V2, V4 and MT of a macaque monkey.

2. What is the major difference between simple and complex cells? Ohzawa et al. examined the effect of binocular disparity on the responses of cells in cat striate cortex. How do simple and complex cells differ from each other in their response to bars at different disparities? (in readings but not discussed in class)

3. Describe what the "aperture problem for pattern translation" is using evidence from cell responses in primate visual areas V1 and MT. Describe a mechanism by which this problem could be solved. Third, describe a higher order 'aperture problem' that is solved as information passes from area MT to area MSTd (i.e., what can't MT see, why can't it see it, and how come MSTd can?). Finally, say briefly why it makes sense to describe color constancy as an 'aperture problem'.

4. Much of the cortex in monkeys (see diagram in Felleman and Van Essen, 1991) consists of patchwork of unimodal sensory areas. The experiment by Haenny, Maunsell, and Schiller, however, suggested that information is readily transferred between different modalities. Describe the Haenny et al. experiment, state their conclusions, and then provide an alternate interpretation also consistent with their data.

5. Make a diagram of an arm with a hand and a muscle showing the names and location of the main types of somatosensory receptors. What basic dichotomy in the time course of the response of different somatosensory receptors is shared with ganglion cell types in the visual and auditory pathways? Why do muscle spindles need their own muscle-spindle-muscles? Describe two situations where muscle spindle and Golgi tendon organ responses will differ.

6. (a) Make a diagram of the dorsal column pathway to somatosensory cortex. (b) Make a diagram showing what receptive field sequence would be expected from a series of penetrations running from anterior to posterior across the finger and palm representations in areas 3b and 1. (draw corresponding views of the cortex and hand). (c) Describe at least 4 experiments suggesting that correlated activity dynamically maintains cortical somatosensory maps.

7. (a) If a moth detects a bat call and accidentally begins to fly toward an attentive bat, will the bat increase or decrease the pitch of its voice? (and why does it do this?) (b) Explain why vowels sound almost the same when the pitch of a person's voice is raised or lowered. (c) What aspect of bat CF/CF processing resembles vowel recognition across human speakers? (d) What does the bat compute from the frequency-modulated parts of its outgoing call and echo? (e) Illustrate the organization of the DSCF area of the bat auditory cortex and trace the expected trajectory of activity elicited by the constant-frequency part of a bat call echo due to the flapping wings of a moth that the bat is approaching.

8. The cochleas transduce sound into neuronal firing patterns distributed across the fibers of the two auditory nerves. (a) Describe the primary stages by which interaural time difference (ITD) is calculated using these two sets of signals and how the phase ambiguity problem is solved (be sure to describe why this problem occurs, and what "characteristic delay" means). (b) What is one similarity between the neural solution to the phase ambiguity problem for interaural time delay and the neural solution to the aperture problem for pattern motion?