Pic Words: February 2007

Human brain, pics and words
Wednesday, February 28, 2007

Humans have a remarkable ability to remember pictures. It was shown several decades ago that people can remember more than 2,000 pictures with at least 90% accuracy in recognition tests over a period of several days, even with short presentation times during learning . This excellent memory for pictures consistently exceeds our ability to remember words . In addition, various manipulations that affect memory performance do so differentially for pictures and words. One such manipulation is the levels of processing effect, which is the advantage for later retrieval of more elaborate or semantic processing of stimuli during encoding . This levels effect is greater for words than for pictures because of superior picture memory even after shallow or nonsemantic encoding . One theory of the mechanism underlying superior picture memory is that pictures automatically engage multiple representations and associations with other knowledge about the world, thus encouraging a more elaborate encoding than occurs with words . This theory implies that there are qualitative differences between the ways words and pictures are processed during memory.

From an evolutionary perspective, the ability to remember various aspects of one’s visual environment must be vital for survival, so it is not surprising that memory for pictorial material is particularly well developed. However, the brain mechanisms underlying this phenomenon are not well understood. Neuroimaging experiments using verbal or nonverbal materials as stimuli have suggested that there are differences in the brain areas participating in the processing of these two kinds of stimulus. For example, previous neuroimaging experiments have shown medial temporal activation during encoding of faces and other nonverbal visual stimuli , but not consistently during encoding of words . Conversely, activation of medial temporal areas has been found during word retrieval , but not consistently during retrieval of nonverbal material . A comparison of recall for words and pictures failed to find any difference between them, but because recall of the name corresponding to the picture also was required, differences between the two conditions may have been reduced . These results suggest differences between the functional neuroanatomy for word and picture memory, but sufficient direct comparisons are lacking. We examined the neural correlates of memory for pictures and words in the context of memory encoding to determine whether material-specific brain networks for memory could be identified. In addition, encoding was carried out under three different sets of instructions to see whether material specificity is a general property of memory or is dependent on how the material is processed.

posted by Dimba @ 4:29 AM, No comment,

Human brain, pics and words

A striking characteristic of human memory is that pictures are remembered better than words. We examined the neural correlates of memory for pictures and words in the context of episodic memory encoding to determine material-specific differences in brain activity patterns. To do this, we used positron emission tomography to map the brain regions active during encoding of words and pictures of objects.
Encoding was carried out by using three different strategies to explore possible interactions between material specificity and types of processing. Encoding of pictures resulted in greater activity of bilateral visual and medial temporal cortices, compared with encoding words, whereas encoding of words was associated with increased activity in prefrontal and temporoparietal regions related to language function. Each encoding strategy was characterized by a distinctive activity pattern, but these patterns were largely the same for pictures and words. Thus, superior overall memory for pictures may be mediated by more effective and automatic engagement of areas important for visual memory, including medial temporal cortex, whereas the mechanisms underlying specific encoding strategies appear to operate similarly on pictures and words.

posted by Dimba @ 4:28 AM, No comment,