encoding

Task determines whether better for neurons to generalize or specialize

July, 2010

A monkey study reveals that, although some neurons are specialized to recognize specific concepts, most are more generalized and these are usually better at categorizing objects.

Previous research has found that individual neurons can become tuned to specific concepts or categories. We can have "cat" neurons, and "car" neurons, and even an “Angelina Jolie” neuron. A new monkey study, however, reveals that although some neurons were more attuned to car images and others to animal images, many neurons were active in both categories. More importantly, these "multitasking" neurons were in fact the best at making correct identifications when the monkey alternated between two category problems. The work could lead to a better understanding of disorders such as autism and schizophrenia in which individuals become overwhelmed by individual stimuli.

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Face coding varies by gender, sexual orientation, & handedness

July, 2010

Why are women better at recognizing faces? Apparently it has to do with using both sides of your brain, and homosexual men tend to do it too.

Why do women tend to be better than men at recognizing faces? Two recent studies give a clue, and also explain inconsistencies in previous research, some of which has found that face recognition mainly happens in the right hemisphere part of the face fusiform area, and some that face recognition occurs bilaterally. One study found that, while men tended to process face recognition in the right hemisphere only, women tended to process the information in both hemispheres. Another study found that both women and gay men tended to use both sides of the brain to process faces (making them faster at retrieving faces), while heterosexual men tended to use only the right. It also found that homosexual males have better face recognition memory than heterosexual males and homosexual women, and that women have better face processing than men. Additionally, left-handed heterosexual participants had better face recognition abilities than left-handed homosexuals, and also tended to be better than right-handed heterosexuals. In other words, bilaterality (using both sides of your brain) seems to make you faster and more accurate at recognizing people, and bilaterality is less likely in right-handers and heterosexual males (and perhaps homosexual women). Previous research has shown that homosexual individuals are 39% more likely to be left-handed.

Reference: 

Proverbio AM, Riva F, Martin E, Zani A (2010) Face Coding Is Bilateral in the Female Brain. PLoS ONE 5(6): e11242. doi:10.1371/journal.pone.0011242

[1611] Brewster, P. W. H., Mullin C. R., Dobrin R. A., & Steeves J. K. E.
(2010).  Sex differences in face processing are mediated by handedness and sexual orientation.
Laterality: Asymmetries of Body, Brain and Cognition.

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One cause of cognitive decline with age

July, 2010

The discovery that a particular type of dendritic spine is lost with age not only provides a target for therapy, but also emphasizes the importance of building skills and expertise when young.

A rhesus monkey study has revealed which dendritic spines are lost with age, providing a new target for therapies to help prevent age-association cognitive impairment. It appears that it is the thin, dynamic spines in the dorsolateral prefrontal cortex, which are key to learning new things, establishing rules, and planning, that are lost. Learning of a new task was correlated with both synapse density and average spine size, but was most strongly predicted by the head volume of thin spines. There was no correlation with size or density of the large, mushroom-shaped spines, which were very stable across age and probably mediate long-term memories, enabling the retention of expertise and skills learned early in life. There was no correlation with any of these spine characteristics once the task was learned. The findings underscore the importance of building skills and broad expertise when young.

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Neural evidence for sudden insight

July, 2010

A rat study supports the idea that rule learning occurs in sudden switches in the activity pattern of neurons, that may be experienced as moments of sudden insight.

A rat study has revealed that as the rats slowly learned a new rule, groups of neurons in the medial frontal cortex switched quite abruptly to a new pattern corresponding directly to the shift in behavior, rather than showing signs of gradual transition. Such sudden neural and behavioral transitions may correspond to so- called "a-ha" moments, and support the idea that rule learning is an evidence-based decision process, perhaps accompanied by moments of sudden insight.

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Human working memory is based on dynamic interaction networks in the brain

April, 2010

Visual working memory, which can only hold three of four objects at a time, is thought to be based on synchronized brain activity across a network of brain regions. Now a new study has allowed us to get a better picture of how exactly that works.

Visual working memory, which can only hold three of four objects at a time, is thought to be based on synchronized brain activity across a network of brain regions. Now a new study has allowed us to get a better picture of how exactly that works. Both the maintenance and the contents of working memory were connected to brief synchronizations of neural activity in alpha, beta and gamma brainwaves across frontoparietal regions that underlie executive and attentional functions and visual areas in the occipital lobe. Most interestingly, individual VWM capacity could be predicted by synchrony in a network centered on the intraparietal sulcus.

Reference: 

[458] Palva, M. J., Monto S., Kulashekhar S., & Palva S.
(2010).  Neuronal synchrony reveals working memory networks and predicts individual memory capacity.
Proceedings of the National Academy of Sciences. 107(16), 7580 - 7585.

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Effects of cue distinctiveness on odor-based context dependent memory

Journal Article: 

Herz, R.S. (1997). The effects of cue distinctiveness on odor-based context dependent memory. Memory and Cognition, 25, 375-380.

  • Smell can aid memory if the same smell is present during the original experience and when you are trying to remember.
  • It works best if the smell is unfamiliar.
  • If the smell is familiar, it is better if it is unusual in the context.

The effect of smell on learning and memory was investigated in an experiment that used three different ambient odors (osmanthus, peppermint, and pine).

Osmanthus was used to see whether there was a difference in performance depending on whether the smell was novel or familiar. Peppermint and pine were used to see whether the appropriateness or inappropriateness of the smell made a difference to memory.

In the experiment, subjects were individually shown into a room in which the odor was present. Their attention was called to the smell, and to ensure their attention to the smell, they were given a questionnaire to fill out about the room environment. They were left alone in the room for ten minutes to promote encoding of contextual cues.

The experimenter then read out a list of 20 common nouns, pausing after each one for the subject to describe an event that the word reminded them of. Memory for the words was tested 48 hours later.

It was found that word recall was best when the novel odor (osmanthus) was present during learning and again at testing. Among the familiar odors, recall was better if the smell was contextually inappropriate (peppermint). The improvement in recall only occurs when the odor is present at both encoding (learning) and retrieval (testing). Clearly, smell is a good contextual cue.

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Encoding features of complex and unfamiliar objects

Journal Article: 

Modigliani, V., Loverock, D.S. & Kirson, S.R. (1998). Encoding features of complex and unfamiliar objects. American Journal Of Psychology, 111, 215-239.

  • We don't store in memory every detail of common objects.
  • Repeated exposures to an object don't necessarily result in remembering any more about them.

There is a pervasive myth that every detail of every experience we've ever had is recorded in memory. It is interesting to note therefore, that even very familiar objects, such as coins, are rarely remembered in accurate detail1.

We see coins every day, but we don't see them. What we remember about coins are global attributes, such as size and color, not the little details, such as which way the head is pointing, what words are written on it, etc. Such details are apparently noted only if the person's attention is specifically drawn to them.

There are several interesting conclusions that can be drawn from studies that have looked at the normal encoding of familiar objects:

  • you don't automatically get more and more detail each time you see a particular object
  • only a limited amount of information is extracted the first time you see the object
  • the various features aren't equally important
  • normally, global rather than detail features are most likely to be remembered

In the present study, four experiments investigated people's memories for drawings of oak leaves. Two different types of oak leaves were used - "red oak" and "white oak". Subjects were shown two drawings for either 5 or 60 seconds. The differences between the two oak leaves varied, either:

  • globally (red vs white leaf), or
  • in terms of a major feature (the same type of leaf, but varying in that twomajor lobes are combined in one leaf but not in the other), or
  • in terms of a minor feature (one small lobe eliminated in one but not in theother).

According to the principle of top-down encoding, the time needed to detect a difference between stimuli that differ in only one critical feature will increase as the level of that feature decreases (from a global to a major specific to a lower-grade specific feature).

The results of this study supported the view that top-down encoding occurs, and indicate that, unless attention is explicitly directed to specific features, the likelihood of encoding such features becomes less the lower its structural level. One of the experiments tested whether the size of the feature made a difference, and it was decided that it didn't.

References

1. Jones, G.V. 1990. Misremembering a familiar object: When left is not right. Memory & Cognition, 18, 174-182.

Jones, G.V. & Martin, M. 1992. Misremembering a familiar object: Mnemonic illusion, not drawing bias. Memory & Cognition, 20, 211-213.

Nickerson, R.S. & Adams, M.J. 1979. Long-term memory of a common object. Cognitive Psychology, 11, 287-307.

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