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Decoding the content of visual short-term memory under distraction in occipital and parietal areas.

Bettencourt KC, Xu Y - Nat. Neurosci. (2015)

Bottom Line: We found that neither distractor presence nor predictability during the memory delay affected behavioral performance.Furthermore, we found no effect of target-distractor similarity on VSTM behavioral performance, further challenging the role of sensory regions in VSTM storage.Overall, consistent with previous univariate findings, our results indicate that superior IPS, but not occipital cortex, has a central role in VSTM storage.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Harvard University, Cambridge, Massachusetts, USA.

ABSTRACT
Recent studies have provided conflicting accounts regarding where in the human brain visual short-term memory (VSTM) content is stored, with strong univariate fMRI responses being reported in superior intraparietal sulcus (IPS), but robust multivariate decoding being reported in occipital cortex. Given the continuous influx of information in everyday vision, VSTM storage under distraction is often required. We found that neither distractor presence nor predictability during the memory delay affected behavioral performance. Similarly, superior IPS exhibited consistent decoding of VSTM content across all distractor manipulations and had multivariate responses that closely tracked behavioral VSTM performance. However, occipital decoding of VSTM content was substantially modulated by distractor presence and predictability. Furthermore, we found no effect of target-distractor similarity on VSTM behavioral performance, further challenging the role of sensory regions in VSTM storage. Overall, consistent with previous univariate findings, our results indicate that superior IPS, but not occipital cortex, has a central role in VSTM storage.

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ROIs and the localizer tasks. A moving, flashing, colored checkerboard wedge (a) and an object-based VSTM task (b) were used to define occipital and parietal topographic regions (c) and superior IPS (d), respectively. In the VSTM task, participants were shown a sequential presentation of either 1, 2, 3, 4, or 6 real world objects at fixation, and, after a brief delay, reported whether the test object shown at fixation was a match or non-match to one of the remembered objects. Superior IPS was defined as a region that tracked the behavioral VSTM capacity measures in this task. IPL and SPL (e) were anatomically defined. Each ROI was further refined to select voxels that respond to the task stimuli. All ROIs are shown here on the inflated left hemisphere of an example participant.
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Figure 2: ROIs and the localizer tasks. A moving, flashing, colored checkerboard wedge (a) and an object-based VSTM task (b) were used to define occipital and parietal topographic regions (c) and superior IPS (d), respectively. In the VSTM task, participants were shown a sequential presentation of either 1, 2, 3, 4, or 6 real world objects at fixation, and, after a brief delay, reported whether the test object shown at fixation was a match or non-match to one of the remembered objects. Superior IPS was defined as a region that tracked the behavioral VSTM capacity measures in this task. IPL and SPL (e) were anatomically defined. Each ROI was further refined to select voxels that respond to the task stimuli. All ROIs are shown here on the inflated left hemisphere of an example participant.

Mentions: MVPA decoding accuracy for the remembered stimulus during the delay period was then examined in our occipital and parietal regions of interest (ROIs; See Fig. 2 and Online Methods) after responses were z-scored within a given ROI to remove any response amplitude differences among the different brain regions. In occipital cortex, when decoding performance was examined in areas V1 through V4 individually, we found no significant interaction between ROI and trial type (F(3,9) = 0.8, p = 0.48). As such, following what was done previously 13, we combined these regions into a single ROI, V1–V4. Replicating Harrison and Tong 13, decoding accuracy for the average delay period in V1–V4 (Fig. 3a) in trials without distractors was significantly above chance (t(9) = 7.1, p < 0.0001). However, for trials with distractors, decoding accuracy dropped significantly compared to trials without distractors (t(9) = 5.6, p = 0.0004) and no longer differed from chance performance (t(9) = 0.8, p = 0.44), even though there was no significant behavioral difference between the two trial types. Although chance level decoding does not necessarily imply the absence of VSTM representation, as limitations of fMRI MVPA could have prevented the readout of weak VSTM representations, the significant drop in the decoding performance, however, unambiguously shows that distractor presence significantly modulated the strength of VSTM representation in occipital cortex.


Decoding the content of visual short-term memory under distraction in occipital and parietal areas.

Bettencourt KC, Xu Y - Nat. Neurosci. (2015)

ROIs and the localizer tasks. A moving, flashing, colored checkerboard wedge (a) and an object-based VSTM task (b) were used to define occipital and parietal topographic regions (c) and superior IPS (d), respectively. In the VSTM task, participants were shown a sequential presentation of either 1, 2, 3, 4, or 6 real world objects at fixation, and, after a brief delay, reported whether the test object shown at fixation was a match or non-match to one of the remembered objects. Superior IPS was defined as a region that tracked the behavioral VSTM capacity measures in this task. IPL and SPL (e) were anatomically defined. Each ROI was further refined to select voxels that respond to the task stimuli. All ROIs are shown here on the inflated left hemisphere of an example participant.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696876&req=5

Figure 2: ROIs and the localizer tasks. A moving, flashing, colored checkerboard wedge (a) and an object-based VSTM task (b) were used to define occipital and parietal topographic regions (c) and superior IPS (d), respectively. In the VSTM task, participants were shown a sequential presentation of either 1, 2, 3, 4, or 6 real world objects at fixation, and, after a brief delay, reported whether the test object shown at fixation was a match or non-match to one of the remembered objects. Superior IPS was defined as a region that tracked the behavioral VSTM capacity measures in this task. IPL and SPL (e) were anatomically defined. Each ROI was further refined to select voxels that respond to the task stimuli. All ROIs are shown here on the inflated left hemisphere of an example participant.
Mentions: MVPA decoding accuracy for the remembered stimulus during the delay period was then examined in our occipital and parietal regions of interest (ROIs; See Fig. 2 and Online Methods) after responses were z-scored within a given ROI to remove any response amplitude differences among the different brain regions. In occipital cortex, when decoding performance was examined in areas V1 through V4 individually, we found no significant interaction between ROI and trial type (F(3,9) = 0.8, p = 0.48). As such, following what was done previously 13, we combined these regions into a single ROI, V1–V4. Replicating Harrison and Tong 13, decoding accuracy for the average delay period in V1–V4 (Fig. 3a) in trials without distractors was significantly above chance (t(9) = 7.1, p < 0.0001). However, for trials with distractors, decoding accuracy dropped significantly compared to trials without distractors (t(9) = 5.6, p = 0.0004) and no longer differed from chance performance (t(9) = 0.8, p = 0.44), even though there was no significant behavioral difference between the two trial types. Although chance level decoding does not necessarily imply the absence of VSTM representation, as limitations of fMRI MVPA could have prevented the readout of weak VSTM representations, the significant drop in the decoding performance, however, unambiguously shows that distractor presence significantly modulated the strength of VSTM representation in occipital cortex.

Bottom Line: We found that neither distractor presence nor predictability during the memory delay affected behavioral performance.Furthermore, we found no effect of target-distractor similarity on VSTM behavioral performance, further challenging the role of sensory regions in VSTM storage.Overall, consistent with previous univariate findings, our results indicate that superior IPS, but not occipital cortex, has a central role in VSTM storage.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, Harvard University, Cambridge, Massachusetts, USA.

ABSTRACT
Recent studies have provided conflicting accounts regarding where in the human brain visual short-term memory (VSTM) content is stored, with strong univariate fMRI responses being reported in superior intraparietal sulcus (IPS), but robust multivariate decoding being reported in occipital cortex. Given the continuous influx of information in everyday vision, VSTM storage under distraction is often required. We found that neither distractor presence nor predictability during the memory delay affected behavioral performance. Similarly, superior IPS exhibited consistent decoding of VSTM content across all distractor manipulations and had multivariate responses that closely tracked behavioral VSTM performance. However, occipital decoding of VSTM content was substantially modulated by distractor presence and predictability. Furthermore, we found no effect of target-distractor similarity on VSTM behavioral performance, further challenging the role of sensory regions in VSTM storage. Overall, consistent with previous univariate findings, our results indicate that superior IPS, but not occipital cortex, has a central role in VSTM storage.

Show MeSH
Related in: MedlinePlus