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The conjunction of non-consciously perceived object identity and spatial position can be retained during a visual short-term memory task
Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI).
Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
2015 (English)In: Frontiers in Psychology, ISSN 1664-1078, E-ISSN 1664-1078, Vol. 6, 1470Article in journal (Refereed) Published
Abstract [en]

Although non-consciously perceived information has previously been assumed to be short-lived (<500 ms), recent findings show that non-consciously perceived information can be maintained for at least 15s Such findings can be explained as working memory without a conscious experience of the information to be retained. However, whether or not working memory can operate on non-consciously perceived information remains controversial, and little is known about the nature of such non-conscious visual short-term memory (VSTM). Here we used continuous flash suppression to render stimuli non-conscious, to investigate the properties of non-consciously perceived representations in delayed match-to-sample (DMS) tasks. In Experiment I we used variable delays (5 or 15s) and found that performance was significantly better than chance and was unaffected by delay duration, thereby replicating previous findings. In Experiment II the DMS task required participants to combine information of spatial position and object identity on a trial-by-trial basis to successfully solve the task. We found that the conjunction of spatial position and object identity was retained, thereby verifying that non-conscious, trial-specific information can be maintained for prospective use. We conclude that our results are consistent with a working memory interpretation, but that more research is needed to verify this interpretation.

Place, publisher, year, edition, pages
Frontiers Media S.A. , 2015. Vol. 6, 1470
Keyword [en]
non-conscious, durability, priming, conscious experience, perception, working memory
National Category
Physiology Applied Psychology
Identifiers
URN: urn:nbn:se:umu:diva-111497DOI: 10.3389/fpsyg.2015.01470ISI: 000363199600001PubMedID: 26483726OAI: oai:DiVA.org:umu-111497DiVA: diva2:875016
Available from: 2015-11-30 Created: 2015-11-13 Last updated: 2016-08-25Bibliographically approved
In thesis
1. The neural substrates of non-conscious working memory
Open this publication in new window or tab >>The neural substrates of non-conscious working memory
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Neurala substrat till icke-medvetet arbetsminne
Abstract [en]

Background: Despite our distinct impression to the contrary, we are only conscious of a fraction of all the neural activity underlying our thoughts and behavior. Most neural processes occur non-consciously, and in parallel with our conscious experience. However, it is still unclear what the limits of non-conscious processes are in terms of higher cognitive functions. Many recent studies have shown that increasingly more advanced functions can operate non-consciously, but non-conscious information is still thought to be fleeting and undetectable within 500 milliseconds. Here we used various techniques to render information non-conscious, together with functional magnetic resonance imaging (fMRI), to investigate if non-consciously presented information can be retained for several seconds, what the neural substrates of such retention are, and if it is consistent with working memory maintenance.

Results: In Study I we used an attentional blink paradigm to render stimuli (single letters) non-conscious, and a variable delay period (5 – 15 s) prior to memory test. It was found that non-conscious memory performance was above chance after all delay durations, and showed no signs of decline over time. Univariate fMRI analysis showed that the durable retention was associated with sustained BOLD signal change in the prefrontal cortex and cerebellum during the delay period. In Study II we used continuous flash suppression (CFS) to render stimuli (faces and tools) non-conscious, and a variable delay period (5 or 15 s) prior to memory test. The durable retention of up to 15 s was replicated, and it was found that stimuli identity and spatial position was retained until prospective use. In Study III we used CFS to render tools non-conscious, and a variable delay period (5 – 15 s) prior to memory test. It was found that memory performance was not better than chance. However, by using multi-voxel pattern analysis it was nonetheless possible to detect the presence vs. absence of non-conscious stimuli in the frontal cortex,and their spatial position (left vs. right) in the occipital cortex during the delay.

Conclusions: Overall these findings suggest that non-consciously presented information (identity and/or position) can be retained for several seconds,and is associated with BOLD signal in frontal and posterior regions. These findings are consistent with working memory maintenance of non-consciously presented information, and thereby constrain models of working memory and theories of consciousness.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. 99 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1835
Keyword
non-conscious, working memory, neural substrates, visual perception, consciousness, functional magnetic resonance imaging (fMRI)
National Category
Neurosciences Psychology
Identifiers
urn:nbn:se:umu:diva-124808 (URN)978-91-7601-53-8 (ISBN)
External cooperation:
Public defence
2016-09-16, Hörsal E, Humanisthuset, Umeå University, 901 87 Umeå, Sweden, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2016-08-26 Created: 2016-08-25 Last updated: 2016-08-25Bibliographically approved

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