Measuring the mind’s private images

Mental imagery, the voluntary retrieval and representation of sensory information from memory, has a fascinating biography. Historically, mental-imagery research suffered criticism because of methodological constraints caused by imagery’s inherent private nature. Recently, many objective research methods have been introduced that allow a more direct investigation into the mechanisms and neural substrates of mental imagery. These new methods have spurred numerous new discoveries, culminating in a flurry of impactful publications over the past few years.

Although imagery played a distinct role in discussions of mental function for thousands of years, empirical work on imagery did not gain strong traction until the last 30 or 40 years. Despite this recent traction, mental-imagery research has still not enjoyed the same degree of investigative attention that other psychological topics have. For example, this graph, shows that the number of articles published each year tfigure_1hat include the phrase “mental imagery” in the title, compared with those that include “visual attention” or “visual working memory,” is relatively low.

In the 1970s cognitive psychologists started to develop tricky methods to measure and study mental imagery objectively. Some of the early discoveries demonstrated a clear relationship between the content of mental images and the time it took to generate or manipulate them (Kosslyn et al., 1978; Shepard et al., 1971). The larger the imagery manipulation, the longer it took to complete, suggesting a correspondence between imagery and physical space.

More recently, there has been a jump in brain-imaging work investigating mental imagery. A recent trend of analyzing the information content of fMRI patterns (instead of the mean amplitude change) has yielded interesting results. This work is often described as decoding because one of the more popular methods trains an algorithm to decode, or make a prediction about, the experimental condition or task, on the basis of the spatial pattern of the fMRI signal across a brain area.

More recently there has been a jump in brain imaging work investigating mental imagery. A recent trend of analysing the information content of fMRI patterns (instead of the mean amplitude change) has yielded interesting results. This work is often described as ‘decoding’, as one of the more popular methods trains an algorithm to decode, or make a prediction about the experimental condition or task, based on the spatial pattern of the fMRI signal across a brain area (Tong et al., 2012).

Recent work from our lab has demonstrated that imagery can facilitate subsequentperception (Pearson et al., 2008). By separating the period of imagery generation and perception in time, the effects of imagery can be examined without the potential confounds of attention (Carrasco et al., 2004). This work demonstrated that when individuals imagine one of two patterns, that pattern has a much higher probability of being perceptually dominant in a subsequent brief binocular rivalry presentation (Pearson et al., 2008; 2011). In other words, the content of the mental image primes subsequent dominance in binocular rivalry – it changes visual awareness of the rivalry display. Binocular rivalry is a visual phenomenon that occurs when two different visual stimuli are presented one to each eye, such that they are forced to coexist at the same visual location. One pattern tends to be dominant over the other, forcing it out of awareness. Binocular rivalry has been a hugely popular tool to study visual awareness in recent times (Tong et al., 2006). However, this work used rivalry as a tool to measure the sensory strength or ‘visual energy’ of mental imagery, enabling individual episodes of imagery to be assessed in an indirect and objective sensory manner. This discovery is also interesting in its own right, as it demonstrates that what we imagine can literally change how we see the world.

To read more on recent developments in objective methods to measure mental imagery check out the recent paper from which some of the above text was taken:

Pearson, J. (2014). New directions in mental imagery research: the binocular rivalry technique and decoding fMRI patterns. Current Directions in Psychological Science. 23(3), 178-183.

 

Or catch my upcoming tutorial at the 2014 ASSC meeting: Seeing what’s not there and measuring it: Conscious perception without a stimulus

 

 

References

Carrasco, M. et al. (2004). Attention alters appearance. Nature neuroscience, 7(3), 308–313. doi:10.1038/nn1194

Kosslyn, S. M. et al. (1978). Visual images preserve metric spatial information: evidence from studies of image scanning. J Exp Psychol Hum Percept Perform, 4(1), 47–60.

Pearson, J. et al. (2008). The functional impact of mental imagery on conscious perception. Current biology : CB, 18(13), 982–986. doi:10.1016/j.cub.2008.05.048

Pearson, J. et al. (2011). Evaluating the Mind’s Eye: The Metacognition of Visual Imagery. Psychol Sci. doi:10.1177/0956797611417134

Shepard, R. N. et al. (1971). Mental rotation of three-dimensional objects. Science (New York, NY), 171(3972), 701–703.

Tong, F. et al. (2006). Neural bases of binocular rivalry. Trends Cogn Sci, 10(11), 502–511. doi:10.1016/j.tics.2006.09.003

Tong, F. et al. (2012). Decoding Patterns of Human Brain Activity. Annual review of psychology, 63(1), 483–509. doi:10.1146/annurev-psych-120710-100412

 

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