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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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Correlation of neural and behavioral VSTM representations from Experiment 4. Six participants from Experiment 1 took part in this experiment. Both V1–V4 (a) and superior IPS (b) show strong negative correlations between behavioral (RT) and neural (decoding accuracy) measures of VSTM representation similarity across the six orientations tested, showing that the more similar a pair of orientation representations are in these brain regions during the VSTM delay period, the harder it is to discriminate them behaviorally in a change-detection task. In V1–V4, two pairs of orientation representations (40º to 160º and 130º to 160º) had identical RTs and decoding accuracies, and so both points occupy the same place in the graph. These results establish a significant link between VSTM representations in both brain regions and behavioral VSTM performance when distractors were absent during the delay period.
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Figure 6: Correlation of neural and behavioral VSTM representations from Experiment 4. Six participants from Experiment 1 took part in this experiment. Both V1–V4 (a) and superior IPS (b) show strong negative correlations between behavioral (RT) and neural (decoding accuracy) measures of VSTM representation similarity across the six orientations tested, showing that the more similar a pair of orientation representations are in these brain regions during the VSTM delay period, the harder it is to discriminate them behaviorally in a change-detection task. In V1–V4, two pairs of orientation representations (40º to 160º and 130º to 160º) had identical RTs and decoding accuracies, and so both points occupy the same place in the graph. These results establish a significant link between VSTM representations in both brain regions and behavioral VSTM performance when distractors were absent during the delay period.

Mentions: Indeed, we found strong negative correlations between decoding and behavioral performance for both V1–V4 and superior IPS (r = −0.7, p = 0.002, and r = −0.59, p = 0.009, respectively, permutation tests for both, see Fig. 6). These results held even if we removed the first time point used for the average delay activity (V1–V4: r = −0.68, p = 0.004; and superior IPS: r = −0.51, p = 0.03, respectively, permutation tests for both), suggesting that these results are not driven by any lingering encoding period activity. Thus, as the VSTM representations in superior IPS and V1–V4 become harder to distinguish, behavioral reaction time increases as well. Combined with the results from the other experiments presented here, this strongly supports the idea that superior IPS plays a central role in the storage of information into VSTM. Being a VSTM region, superior IPS is unlikely to be involved in the initial computation and representations of the orientation information. Rather, such information must be processed elsewhere (e.g., V1–V4) and uploaded into superior IPS when it needs to be retained in VSTM. It is thus not surprising that delay representations in V1–V4 also correlated with behavioral performance. However, Experiment 1 clearly shows that such representations cannot reliably support successful information retention in VSTM.


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

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

Correlation of neural and behavioral VSTM representations from Experiment 4. Six participants from Experiment 1 took part in this experiment. Both V1–V4 (a) and superior IPS (b) show strong negative correlations between behavioral (RT) and neural (decoding accuracy) measures of VSTM representation similarity across the six orientations tested, showing that the more similar a pair of orientation representations are in these brain regions during the VSTM delay period, the harder it is to discriminate them behaviorally in a change-detection task. In V1–V4, two pairs of orientation representations (40º to 160º and 130º to 160º) had identical RTs and decoding accuracies, and so both points occupy the same place in the graph. These results establish a significant link between VSTM representations in both brain regions and behavioral VSTM performance when distractors were absent during the delay period.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4696876&req=5

Figure 6: Correlation of neural and behavioral VSTM representations from Experiment 4. Six participants from Experiment 1 took part in this experiment. Both V1–V4 (a) and superior IPS (b) show strong negative correlations between behavioral (RT) and neural (decoding accuracy) measures of VSTM representation similarity across the six orientations tested, showing that the more similar a pair of orientation representations are in these brain regions during the VSTM delay period, the harder it is to discriminate them behaviorally in a change-detection task. In V1–V4, two pairs of orientation representations (40º to 160º and 130º to 160º) had identical RTs and decoding accuracies, and so both points occupy the same place in the graph. These results establish a significant link between VSTM representations in both brain regions and behavioral VSTM performance when distractors were absent during the delay period.
Mentions: Indeed, we found strong negative correlations between decoding and behavioral performance for both V1–V4 and superior IPS (r = −0.7, p = 0.002, and r = −0.59, p = 0.009, respectively, permutation tests for both, see Fig. 6). These results held even if we removed the first time point used for the average delay activity (V1–V4: r = −0.68, p = 0.004; and superior IPS: r = −0.51, p = 0.03, respectively, permutation tests for both), suggesting that these results are not driven by any lingering encoding period activity. Thus, as the VSTM representations in superior IPS and V1–V4 become harder to distinguish, behavioral reaction time increases as well. Combined with the results from the other experiments presented here, this strongly supports the idea that superior IPS plays a central role in the storage of information into VSTM. Being a VSTM region, superior IPS is unlikely to be involved in the initial computation and representations of the orientation information. Rather, such information must be processed elsewhere (e.g., V1–V4) and uploaded into superior IPS when it needs to be retained in VSTM. It is thus not surprising that delay representations in V1–V4 also correlated with behavioral performance. However, Experiment 1 clearly shows that such representations cannot reliably support successful information retention in VSTM.

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