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Visual masking in magnetic resonance imaging.
Stockholm University, Faculty of Social Sciences, Department of Psychology.
2005 (English)In: Neuroimage, ISSN 1053-8119, Vol. 27, no 2, 465-7 p.Article in journal (Refereed) Published
Abstract [en]

When a brief target picture is followed by another picture (mask),

people often report that they are not consciously aware of the target.

Thus, visual masking can be used to manipulate perceptual awareness

of target pictures. To avoid interference with magnetic resonance

imaging, pictures have been presented on liquid crystal device (LCD)

and thin film transistor (TFT) projectors that were placed outside of the

scanner room. However, we found that display devices with LCD/TFT

technology exhibit poor accuracy in presenting pictures at brief

durations [Wiens, S., Fransson, P., Dietrich, T., Lohmann, P., Ingvar,

M., O¨ hman, A., 2004. Keeping it short: A comparison of methods for

brief picture presentation. Psychological Science, 15, 282–285]. In this

paper, we present a reliable and valid masking procedure involving two

LCD/TFT projectors in combination with mechanical shutters. Because

LCD/TFT projectors present pictures in steady state at longer durations

(e.g., after 70 ms), picture presentation is more ecologically valid than

for common cathode ray tube (CRT) monitors that present pictures in

multiples of refresh cycles. Also, because picture presentation with

mechanical shutters is instantaneous and reliable in terms of onset, rise

time, and duration, shutters can be used to control picture durations

precisely in steps of milliseconds. In this paper, we also discuss risks for

confounding effects from unreliable picture presentations in masking.

Our findings and arguments recommend the use of mechanical shutters

in front of LCD/TFT projectors in imaging studies of visual masking.

Place, publisher, year, edition, pages
2005. Vol. 27, no 2, 465-7 p.
Keyword [en]
Humans, Magnetic Resonance Imaging/instrumentation/*methods, Photic Stimulation/*methods, Reproducibility of Results, Transistors, Visual Perception/*physiology
URN: urn:nbn:se:su:diva-19270PubMedID: 15882953OAI: diva2:185794
Available from: 2008-01-15 Created: 2008-01-15 Last updated: 2011-01-12Bibliographically approved

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