> Learning to see consciously > > March 9th, 2011 in Medicine & Health / Neuroscience > Training for conscious perception: A. Subjects are presented with geometric > forms in rapid succession. After 10 milliseconds the forms were masked to > render them invisible. The task of the subjects was to judge their > visibility. B. Location of form and mask on the screen. C. A square and a > diamond serve as the visual cues, a star as a mask. Credit: PNAS Early > Edition, doi: 10.1073/pnas.1009147108 > > Our brains process many more stimuli than we become aware of. Often images > enter our brain without being noticed: visual information is being processed, > but does not reach consciousness, that is, we do not have an impression of > it. Then, what is the difference between conscious and unconscious > perception, and can both forms of perception be changed through practice? > These questions are important not only for basic research, but also for the > treatment of patients with perceptual deficits due to brain lesions e.g. > following a stroke. Scientists at the MPI for Brain Research in > Frankfurt/Main could now show that seeing can be trained. Their tests > revealed that the brain regions underlying the learning effects on conscious > perception are different than the ones underlying the learning effects on the > mere processing of stimuli. > > Visual stimuli undergo a series of processing stages on their journey from > the eye to the brain. How conscious perception can arise from the activity of > neurons is one of the mysteries that the neurophysiologists at the MPI for > Brain Research seek to solve. “Today, we know that the processing of stimuli > in the cortex remains extremely plastic, or malleable, even in adults,” > explains Caspar Schwiedrzik who investigates the neural mechanisms of visual > perception with his Max Planck colleagues Wolf Singer and Lucia Melloni. In > their current study, the scientists examined whether perception can be > influenced by long-term and systematic training and whether such training > does not only change the processing, but also affects whether the stimulus > can be consciously perceived. > > It is known from clinical studies that some stroke patients who suffer > partial blindness as a result of damage to the visual cortex can discriminate > between stimuli that fall into their blind visual field. This unconscious > discrimination ability can be improved through training. Nevertheless, the > patients report that they do not see the images. In a few cases, however, > conscious perception of the stimuli could be improved with training. Is it > maybe possible to learn to “see consciously”? > > To investigate this question in healthy subjects, the Frankfurt scientists > developed an experimental set up with which different learning effects on > perception could be measured. The subjects were shown images of two different > geometric forms – a square and a diamond – on a screen in rapid succession > and in a random sequence, and were asked to discriminate between them. The > visibility of the images was limited by presenting a mask shortly after each > image, which rendered the shape invisible. > > The experiment was designed such that the subjects could initially not > discriminate between the images and that they were also subjectively > invisible. The subjects were then trained for several days. Each round of the > training involved the presentation of images followed by the mask. As soon as > the subject indicated by pressing a button which form had been shown and how > clearly he or she had seen the form, the next stimulus and the next mask were > shown. This process was repeated 600 times per day. After several days, the > subjects could better discriminate between the target stimuli. From the > ratings of the visibility of the stimuli, the scientists could further > conclude that the participants’ subjective perception had increased as well: > the images now entered consciousness. Thus, the scientists succeeded in > demonstrating that it is also possible to learn to see consciously. > > The question remained, however, as to how objective and not necessarily > conscious processing of stimuli and their subjective, conscious perception > are linked. To gain a better understanding of the individual processing steps > and to localize them in the brain, the experiment was repeated once more. > This time, the image and mask were shown on a different part of the screen, > and were thus processed by a different part of the brain. “The results were > revealing,” explains Lucia Melloni: “While the learning effect for the pure > processing of the stimuli, that is the discrimination of the shape, was lost > with the spatial rearrangement of the stimuli, the clearer visibility of the > images, that is the learning effect in terms of conscious seeing, remained.” > Therefore, objective processing and subjective perception of the stimuli seem > to be less closely linked than previously assumed. The two training effects > appear to be based on two different areas of the brain. > > “Our experiments have shown that the neuronal processes that underlie > conscious perception are very flexible,” Schwiedrzik concludes. The findings > provide important insights for medical applications, in particular for the > rehabilitation of people suffering from perceptual deficits caused by brain > lesions. > > More information: Caspar M. Schwiedrzik, et al. Subjective and objective > learning effects dissociate in space and in time. PNAS Early Edition, > doi:10.1073/pnas.1009147108 > > Provided by Max-Planck-Gesellschaft > > > "Learning to see consciously." March 9th, 2011. > http://www.physorg.com/news/2011-03-consciously.html >
