Maartje C. de Jong - PhD thesis

Neural mechanisms underlying temporal modulation of visual perception.

(summary in Dutch / Samenvatting in het Nederlands)

However confident we feel about the way we perceive the visual world around us, there is not a one-to-one relation between visual stimulation and visual perception. Our eyes register reflections of the visual environment and our brain has the difficult task of constructing 'reality' from this information. In doing so, the brain has to rely on internal information, like inferences and assumptions.

In my PhD thesis I use fMRI, EEG and intracranial recording in humans to measure brain activity while participants observe ambiguous images, i.e., images that elicit two mutually exclusive perceptual interpretations. Because perception of these images changes over time while the image remains the same, it is possible to study neural activations associated with internal influences on perception while the external factors as constant. I found that internal information - like perceptual memory and the resolvement of perceptual ambiguity - is associated with activations of sensory rather than cognitive brain regions.

Given the known role of these sensory regions in the processing of external information (the image), our findings indicate that internal and external contributions to perception are not processed in separate brain regions. Instead, they are inextricably linked in terms of neural processing. It thus seems that objective perceptual processing based solely on external information does not occur in the brain.

A dance about my PhD project won the AAAS 'Dance Your PhD' contest 2010 in the category Biology (see [Science magazine] and [explanation of the dance]):


[read] PDF of the thesis

[read] Article about my PhD thesis
by Netherlands Organisation for Scientific Research
(in Dutch)

[read] Article about my PhD research by Kennislink (in Dutch)

One of the internal factors I studied is perceptual memory. I found that the way we perceive an ambiguous image is partly determined by the way we have perceived it in the preceeding couple of minutes.   [PDF].

I also found that perceptual memory modulates neural processing soon after the onset of the stimulus, preceding the completion of the perceptual interpretation. I observed this using electro-encephalography, a technique that measures neural activity at a high temporal resolution.   [PDF]

In another study I used functional magnetic resonance imaging, a technique with a high spatial rather than temporal resolution. Perceptual memory was associated with activations in sensory brain regions located in the occipital lobe. Moreover, the involved sensory brain regions differed between stimuli and, per stimulus, were specialized in the processing of that stimulus specifically. Perceptual memory is thus processed in brain regions that are also dedicated to the processing of stimulus-specific external information.   [PDF]