Copyright © 2006 by Allyn and Bacon Chapter 7 Mechanisms of Perception, Conscious Awareness, and Attention How You Know the World This multimedia product and its contents are protected under copyright law. The following are prohibited by law: any public performance or display, including transmission of any image over a network; preparation of any derivative work, including the extraction, in whole or in part, of any images; any rental, lease, or lending of the program.

Sensory Areas of the Cortex  Primary – input mainly from thalamic relay nuclei For example, striate cortex receives input from LGN  Secondary –input mainly from primary and secondary cortex within the sensory system  Association – input from more than one sensory system, usually from secondary sensory cortex

Principles Guiding the Interactions of Sensory Cortex  Hierarchical Organization Specificity and complexity increases with each level Sensation – detecting a stimulus Perception – understanding the stimulus  Functional Segregation  Parallel Processing

Visual Cortex  Primary (V1) – posterior occipital lobe  Secondary Prestriate cortex – a band of tissue surrounding V1 Inferotemporal cortex  Tertiary – various areas, largest single area is in posterior parietal cortex

Blindsight  The ability to respond to a visual stimulus even with no conscious awareness of the stimulus (due to a scotoma)  May be that some connections still exist in V1, allowing for reactions without awareness  May be that message gets to the brain by connections that do not pass through the scotoma (i.e., LGN to V2)

Dorsal and Ventral Streams  Dorsal stream – “where”/control of behavior V1 to dorsal prestriate cortex to posterior parietal  Ventral stream – “what”/conscious perception V1 to ventral prestriate cortex to inferotemporal cortex  Both “where”/“what” and behavior/perception distinctions are supported by effects of damage

Prosopagnosia  supports the “control of behavior” vs “conscious perception” theory  Agnosia – failure of recognition  Visual agnosia – able to see, but unable to recognize  Prosopagnosia – an agnosia for faces

Prosopagnosia  Prosopagnosics are unable to recognize particular faces – they also are unable to recognize other specifics – which chair, which cow, etc.  There is an inability to recognize specific objects belonging to a complex class of objects  Note – some cases where deficits are limited to faces have been observed

Prosopagnosia  A result of bilateral damage to the ventral “what”/conscious perception stream  Thus, unconscious recognition can be hypothesized  And has been supported – altered skin conductance responses to familiar Vs unfamiliar faces

Recognizing Specific Classes of Objects  Fusiform face area – activity increased during face recognition but not recognition of other objects  Areas in ventral stream may be specific to humans, cats, or houses or sheep  But – more than one area responds to each class and there is great overlap

Somatosensory Agnosias  Asterognosia – inability to recognize objects by touch pure cases are rare – other sensory deficits are usually present  Asomatognosia – the failure to recognize parts of one’s own body – the case of the man who fell out of bed

The Paradoxes of Pain  Despite its unpleasantness, pain is adaptive and needed  No obvious cortical representation (although the anterior cingulate gyrus appears involved in emotional component)  Descending pain control – pain can be suppressed by cognitive and emotional factors

Identifying a Descending Pain Control Circuit  3 discoveries made this possible Electrical stimulation of the periaqueductal gray (PAG) has analgesic (pain-blocking) effects PAG and other brain areas have opiate receptors Existence of endogenous opiates (natural analgesics) - endorphins

Brain Damage and the Chemical Senses  Anosmia – inability to smell Most common cause is a blow to the head that damages olfactory nerves Incomplete deficits seen with a variety of disorders  Ageusia – inability to taste Rare due to multiple pathways carrying taste information

Selective Attention  Cocktail phenomenon – indicates that there is processing of information not attended to  Why would a man be unable to see two objects simultaneously when he can see each individually?  Simultanagnosia – a difficulty attending to more than one visual object at a time – cause?  Bilateral damage to the dorsal stream (involved with localizing objects in space)