Psychology of Language

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Tabitha Quinn
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1 PSYCH 150 / LIN 155 UCI COGNITIVE SCIENCES syn lab Psychology of Language Prof. Jon Sprouse : Extra slides about animal brains 1

2 Comparative primatology in search of the biological foundation of language 2

3 Language area homologs in chimpanzee cortex? Brodmann area 44, the posterior portion of Broca s area (in LiFG), may generally be larger in the left hemisphere than the right hemisphere, at least for males: Amunts et al studied 5 males and 5 females, and found that all of the males showed a larger left area 44 than right area 44. Area 45 in males showed no differences in size based on hemisphere. Females showed no reliable pattern for either area 44 or area 45. 3

Language area homologs in chimpanzee cortex? The homologue of Broadmann area 44 in non-human primates (20 chimpanzees, 5 Bonobos, and 2 Gorillas) also seems to show a left>right asymmetry.

4 Language area homologs in chimpanzee cortex? The homologue of Broadmann area 44 in non-human primates (20 chimpanzees, 5 Bonobos, and 2 Gorillas) also seems to show a left>right asymmetry. Cantalupo and Hopkins 2001 used MRI to study hemispheric differences in size of area 44. This chart shows the direction and magnitude of the asymmetries for each subject (split into groups by species). In total, 20 primates showed a larger left hemisphere area 44. 4

Language area homologs in chimpanzee cortex? Taglialela et al. 2008 used PET (positron emission tomography) to study communicative signaling (gestures and calls) in captive chimpanzees.

5 Language area homologs in chimpanzee cortex? Taglialela et al used PET (positron emission tomography) to study communicative signaling (gestures and calls) in captive chimpanzees. These images show a lateralization comparison: bright spots indicate areas where activity in that hemisphere was greater than activity in the other hemisphere. The results indicate that the homologue of left Broca s area (44/45) is more active than the homolog of right Broca s area during communicative signaling. There also appears to be increased activation in left temporal lobe. 5

6 But, recent findings cast doubt on the asymmetry in chimpanzees Schenker et al performed post-mortem analyses of 12 chimpanzee brains in an attempt to look at the hemispheric asymmetries in more detail. Here are some examples of the MR images that they collected of the post-mortem brains 6

7 But, recent findings cast doubt on the asymmetry in chimpanzees Schenker et al performed post-mortem analyses of 12 chimpanzee brains in an attempt to look at the hemispheric asymmetries in more detail. When they compared the volume of areas 44 and 45 across both hemispheres, they found no statistically significant difference between hemispheres for either area. This makes it possible once again that the increased size of left Broca s area in humans is critical to our unique language abilities. 7

8 But, recent findings cast doubt on the asymmetry in chimpanzees Schenker et al performed post-mortem analyses of 12 chimpanzee brains in an attempt to look at the hemispheric asymmetries in more detail. They also compared individual variation (in the size of the areas) in chimpanzees to individual variation in humans, and found a similar level of variation in both species. 8

9 Mirror Neurons 9

What are mirror neurons? Mirror neurons are a population of neurons in macaques that respond to two things: 1. 2.

10 What are mirror neurons? Mirror neurons are a population of neurons in macaques that respond to two things: The act of reaching for or grasping an object (goal-directed action) The perception of someone else reaching for or grasping an object (perceiving a goal-directed action) Mirror neurons are found in a subsection of macaque pre-motor cortex called F5. Current estimates suggest that mirror neurons make up about 17% of the neurons in F5. 10

The defining properties of MNs In order to be a mirror neuron, a cell must exhibit mirror activity: 1. 2.

11 The defining properties of MNs In order to be a mirror neuron, a cell must exhibit mirror activity: Respond to both an action and the perception of that action Respond only during the action/perception itself. Any activity before or after could be movement preparation, which is by definition not mirror activity. Mirror neurons must also be selectively associated with the action, and not aspects that are related to the action: They do not respond to the objects involved in the action when presented in isolation They do not respond to mimicking of the action (pantomime) 11

12 The claim is that mirror neurons encode action understanding Mirror neurons have really only been identified for goal-directed-actions, such as grasping for an object, or placing an object in the mouth They do not respond to non-goal-directed actions like grasping without an object present They do not respond to emotional gestures, like flailing This specificity has led some researchers to propose that mirror neurons are the basis for action understanding. The idea is that goal-directed-actions have a semantics, perhaps the very idea of a goal or intention. Under this theory, mirror neurons encode this semantics - a high level mental representation. This is why they respond to both the action itself, and the perception of the action, because both rely on the semantics of the action. 12

13 Do humans have mirror neurons? The human homologue of F5 would be sections of the premotor cortex and LiFG such as the inferior portion of BA 6 and our old friend BA 44: 13

14 Do humans have mirror neurons? This is a hotly contested debate right now. In order to identify mirror neurons, we need to find areas that exhibit mirror activity: 1. Rizolatti et al found that Broca s area is active during the perception of goal-directed actions, but not during the production of goal-oriented actions. 2. Rizolatti and Craighero 2004 found that Broca s area is active to imitation; but adult macaques don t imitate, so this is not part of monkey mirror activity 3. Gainotti and Lemmo 1976 observed pantomime deficits in aphasia; but pantomime is (by definition) not part of monkey mirror activity 4. Morin and Grezes 2008, in a meta-analysis of fmri studies, found that Broca s area does not distinguish between goal-directed and non-goaldirected actions. 14

15 Do mirror neurons encode action understanding for humans? Again, this is a hotly contested debate right now. In order to test this theory, we need to find evidence that action understanding is dependent upon the mirror system: Buccino et al found that Broca s area is active to videos of a human talking (no sound) and a monkey lip-smacking (no sound), but not a dog barking. The question is whether subjects understood the action meaning of all three activities, or not. Pazzaglia et al found that patients with limb apraxia (paralysis) showed a correlation between inability to discriminate the correctness of a gesture and the inability to perform the gesture in 14 out of 21 patients. However, 7 out of 21 patients showed no discrimination deficit at all, so the question is whether they are proof that comprehension and production dissociate or not. There are tons more studies like this, where the question is whether an incomplete association between Broca s area and action comprehension/ production is evidence for the theory, or evidence against the theory! 15

Motor Theories of Cognition

Motor Theories of Cognition In his Essay Towards a New Theory of Vision (1709) Berkeley uses a motor representation to describe depth perception. Motor theory in Movement and Mental Imagery (1916) by Margeret