CH 3 & 4 - VISION & OTHER SENSES

4. Snyder: Describe at least two auditory paradigms that are useful for studying auditory awareness and which visual paradigms if any to which they are similar (Hint: you might need to search a bit in the literature or other readings)? Does auditory awareness seem to work similarly to visual awareness?

Change deafness is when people listen to several auditory objects at the same time and fail to detect the addition, deletion, or replacement of one of an auditory object. This is similar to change blindness in the visual domain and similar neural correlates of successful change detection are found in both paradigms. Auditory stream segregation is when people listen to two tones alternating in frequency or other characteristic and can hear the tones as one melody going up and down in frequency or two separate stream-like objects of tones; perception is usually first heard as one stream, but after switching to two streams, perception can switch back and forth (as with other rivalry paradigms such as moving plaid and Necker cube).

5. Ghazanfar: What brain areas do classical theories propose to be multisensory? What additional areas are multisensory according to this article? What role do brain oscillations play in multisensory integration (Hint: use this article to see what articles have been published more recently than 2006 on this topic)?

Prior research focused on a small number of cortical (superior temporal sulcus, intraparietal cortex, premotor cortex) and subcortical areas (superior colliculus, amygdala) as integrating information between different senses for very specific uses (eye movements, emotion processing). This article claims that early sensory areas (including secondary auditory and visual areas) receive input from other senses, much like these areas receive top-down input from frontal and parietal areas for the purpose of attention modulation. Brain oscillations might be important for creating brief time windows in which information can be integrated across senses, as evidenced by studies by Schroeder and his colleagues.

3. Hochstein: How is the reverse hierarchy theory (RHT) similar and different from classic views of visual processing (e.g., Hubel & Wiesel)?

RHT claims that-- at least in the ventral stream-- bottom-up visual processing is largely automatic and unconscious, with more complex features being detected as information goes up the hierarchy of brain areas (V1àV2àV4àIT) until it reaches the top, which can lead to consciousness (e.g., using neurons in IT that detect whole objects or scenes). This is referred to as vision at a glance and is probably sufficient for some search tasks and for appreciating what type of object or scene is being viewed. However, for tasks that require more detail (difficult search tasks, change detection), activity in lower level areas must be activated by top-down connections from higher levels to access neurons that detect the types of details needed.

1. Goodale: Where are the dorsal and ventral streams of the visual system? What are the functions of the dorsal and ventral streams, as proposed by Ungerleider and Mishkin vs. as proposed by Goodale and Milner?

The dorsal and ventral streams are in the superior parietal lobe and inferotemporal cortex, respectively, and arise from common inputs from early visual areas (V1, V2, etc.). Ungerleider and Mishkin proposed that the dorsal stream is important for identifying where objects are in space and that the ventral stream is important for identifying object identity. Goodale and Milner proposed something similar, except they claimed that the dorsal stream is important for using visual information to guide action (eye movements, reaching, grasping), rather than just passively perceiving spatial properties of objects.

2. Tong: Based on studies of binocular rivalry in humans and monkeys, what parts of the brain are most involved in visual awareness or consciousness? What types of representations and connections between neurons or brain areas are important for visual awareness?

Tong argues that binocular rivalry arises from a number of different brain areas that likely interact with each other. In particular, sets of neurons that are selective for one eye or the other (monocular neurons) can compete with each other to decide which eye's stimulus will be consciously perceived at a given time. This competition is the result of one eye's neurons inhibiting the other eye's neurons (e.g., in LGN and V1). Over time, this inhibition undergoes adaptation until the inhibition is no longer strong enough and the other eye's neurons begin to drive perception. Also, if the monocular competition is not complete, higher-level neurons (e.g., in inferotemoral cortex) that represent the actual patterns can compete with each other. Feedback from higher to lower level neurons might also be important for effects of attention and other high-level influences on perception.