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Motion along the mental number line reveals shared representations for numerosity and space.

Schwiedrzik CM, Bernstein B, Melloni L - Elife (2016)

Bottom Line: Do such 'recycled' circuits retain their original functionality?The reference frame of this effect is spatiotopic.Together with the tuning properties of the effect this suggests that motion direction-numerosity cross-adaptation may occur in a homolog of area LIP. 'Cortical recycling' thus expands but does not obliterate the functions originally performed by the recycled circuit, allowing for shared computations across domains.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Neural Systems, The Rockefeller University, New York, United States.

ABSTRACT
Perception of number and space are tightly intertwined. It has been proposed that this is due to 'cortical recycling', where numerosity processing takes over circuits originally processing space. Do such 'recycled' circuits retain their original functionality? Here, we investigate interactions between numerosity and motion direction, two functions that both localize to parietal cortex. We describe a new phenomenon in which visual motion direction adapts nonsymbolic numerosity perception, giving rise to a repulsive aftereffect: motion to the left adapts small numbers, leading to overestimation of numerosity, while motion to the right adapts large numbers, resulting in underestimation. The reference frame of this effect is spatiotopic. Together with the tuning properties of the effect this suggests that motion direction-numerosity cross-adaptation may occur in a homolog of area LIP. 'Cortical recycling' thus expands but does not obliterate the functions originally performed by the recycled circuit, allowing for shared computations across domains.

No MeSH data available.


Related in: MedlinePlus

Hypothetical effect of adaptation on numerosity-encoding neurons in LIP and VIP.It has been shown that area LIP (dotted lines) contains neurons that encode numerosity with monotonically increasing firing rates, i.e., the larger the number of dots in the display, the more vigorous the neural response (Roitman et al., 2007). In contrast, one stage downstream from area LIP, neurons are narrowly tuned to numerosity in area VIP (solid lines), i.e., each neuron will respond vigorously only to a narrow range of numerosities, and less so when either more or less dots are displayed (Nieder et al., 2006). Adaptation has different effects on these different classes of tuning curves (black lines): In area VIP, adaptation will only affect neurons that encode the number of dots in the adapter (400 in Experiment 1) while neurons coding for numerosities far removed from the adapter, such as the ones in the test (23:107 in Experiment 1) and probe dot clouds (30 in Experiment 1), will not be affected. In contrast, in area LIP, adaptation will shift the entire tuning curve, hence even adaptation to 400 dots affects responses to numerosities in the range of 23:107. Thus, the adaptation effect we observe is likely to arise in area LIP, not VIP.DOI:http://dx.doi.org/10.7554/eLife.10806.009
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fig3: Hypothetical effect of adaptation on numerosity-encoding neurons in LIP and VIP.It has been shown that area LIP (dotted lines) contains neurons that encode numerosity with monotonically increasing firing rates, i.e., the larger the number of dots in the display, the more vigorous the neural response (Roitman et al., 2007). In contrast, one stage downstream from area LIP, neurons are narrowly tuned to numerosity in area VIP (solid lines), i.e., each neuron will respond vigorously only to a narrow range of numerosities, and less so when either more or less dots are displayed (Nieder et al., 2006). Adaptation has different effects on these different classes of tuning curves (black lines): In area VIP, adaptation will only affect neurons that encode the number of dots in the adapter (400 in Experiment 1) while neurons coding for numerosities far removed from the adapter, such as the ones in the test (23:107 in Experiment 1) and probe dot clouds (30 in Experiment 1), will not be affected. In contrast, in area LIP, adaptation will shift the entire tuning curve, hence even adaptation to 400 dots affects responses to numerosities in the range of 23:107. Thus, the adaptation effect we observe is likely to arise in area LIP, not VIP.DOI:http://dx.doi.org/10.7554/eLife.10806.009

Mentions: Together, Experiments 1–4 indicate that recycled numerosity circuits continue to process purely spatial features. Where could this effect arise? In monkeys, the first stage of number processing is in the intraparietal sulcus (IPS), specifically in areas LIP and VIP (Nieder and Dehaene, 2009). Comparing our psychophysical results to the known numerosity tuning functions of these two areas gives a first indication of where and how this cross-adaptation effect may come about (Figure 3): Because we were able to exert an adaption effect despite a large difference between the number of adapting dots (e.g., 400 in Experiment 1) and the number of dots in the test/probe display (e.g., 23:107; 30 in Experiment 1), the tuning functions of the involved neurons must be rather broad. Such broad tuning curves for numerosity have been found in monkey area LIP, where neurons show monotonic increases and decreases in firing rate with the number of items in a display (Roitman et al., 2007) and are also sensitive to motion direction (Fanini and Assad, 2009). LIP is thought to correspond to an intermediate analog representation of numerosity before the cardinal representation of number arises (Dehaene and Changeux, 1993; Verguts and Fias, 2004) downstream in area VIP, which is also sensitive to motion (Colby et al., 1993) but where numerosity neurons show much narrower tuning functions (Nieder and Dehaene, 2009). If adaptation arose in VIP, the strongest effects should occur directly around the adaptor, but fall off the further the adaptor is removed from the test/probe (Robbins et al., 2007; Webster, 2011). In contrast, we found that adapting and probing with the same number of dots (30 in Experiment 5) did not lead to a significant motion direction-specific aftereffect (mean difference right vs. left −3.69, p=0.92, Wilcoxon signed rank test, one-sided; Bayesian posterior probability <0.18%). The presence of a strong adaptation effect when adapting with 400 and testing with 30 dots and the absence of an adaptation effect when adapting and testing with 30 dots together indicate that motion direction-numerosity cross-adaptation may arise in a human homolog of area LIP.10.7554/eLife.10806.009Figure 3.Hypothetical effect of adaptation on numerosity-encoding neurons in LIP and VIP.


Motion along the mental number line reveals shared representations for numerosity and space.

Schwiedrzik CM, Bernstein B, Melloni L - Elife (2016)

Hypothetical effect of adaptation on numerosity-encoding neurons in LIP and VIP.It has been shown that area LIP (dotted lines) contains neurons that encode numerosity with monotonically increasing firing rates, i.e., the larger the number of dots in the display, the more vigorous the neural response (Roitman et al., 2007). In contrast, one stage downstream from area LIP, neurons are narrowly tuned to numerosity in area VIP (solid lines), i.e., each neuron will respond vigorously only to a narrow range of numerosities, and less so when either more or less dots are displayed (Nieder et al., 2006). Adaptation has different effects on these different classes of tuning curves (black lines): In area VIP, adaptation will only affect neurons that encode the number of dots in the adapter (400 in Experiment 1) while neurons coding for numerosities far removed from the adapter, such as the ones in the test (23:107 in Experiment 1) and probe dot clouds (30 in Experiment 1), will not be affected. In contrast, in area LIP, adaptation will shift the entire tuning curve, hence even adaptation to 400 dots affects responses to numerosities in the range of 23:107. Thus, the adaptation effect we observe is likely to arise in area LIP, not VIP.DOI:http://dx.doi.org/10.7554/eLife.10806.009
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Related In: Results  -  Collection

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fig3: Hypothetical effect of adaptation on numerosity-encoding neurons in LIP and VIP.It has been shown that area LIP (dotted lines) contains neurons that encode numerosity with monotonically increasing firing rates, i.e., the larger the number of dots in the display, the more vigorous the neural response (Roitman et al., 2007). In contrast, one stage downstream from area LIP, neurons are narrowly tuned to numerosity in area VIP (solid lines), i.e., each neuron will respond vigorously only to a narrow range of numerosities, and less so when either more or less dots are displayed (Nieder et al., 2006). Adaptation has different effects on these different classes of tuning curves (black lines): In area VIP, adaptation will only affect neurons that encode the number of dots in the adapter (400 in Experiment 1) while neurons coding for numerosities far removed from the adapter, such as the ones in the test (23:107 in Experiment 1) and probe dot clouds (30 in Experiment 1), will not be affected. In contrast, in area LIP, adaptation will shift the entire tuning curve, hence even adaptation to 400 dots affects responses to numerosities in the range of 23:107. Thus, the adaptation effect we observe is likely to arise in area LIP, not VIP.DOI:http://dx.doi.org/10.7554/eLife.10806.009
Mentions: Together, Experiments 1–4 indicate that recycled numerosity circuits continue to process purely spatial features. Where could this effect arise? In monkeys, the first stage of number processing is in the intraparietal sulcus (IPS), specifically in areas LIP and VIP (Nieder and Dehaene, 2009). Comparing our psychophysical results to the known numerosity tuning functions of these two areas gives a first indication of where and how this cross-adaptation effect may come about (Figure 3): Because we were able to exert an adaption effect despite a large difference between the number of adapting dots (e.g., 400 in Experiment 1) and the number of dots in the test/probe display (e.g., 23:107; 30 in Experiment 1), the tuning functions of the involved neurons must be rather broad. Such broad tuning curves for numerosity have been found in monkey area LIP, where neurons show monotonic increases and decreases in firing rate with the number of items in a display (Roitman et al., 2007) and are also sensitive to motion direction (Fanini and Assad, 2009). LIP is thought to correspond to an intermediate analog representation of numerosity before the cardinal representation of number arises (Dehaene and Changeux, 1993; Verguts and Fias, 2004) downstream in area VIP, which is also sensitive to motion (Colby et al., 1993) but where numerosity neurons show much narrower tuning functions (Nieder and Dehaene, 2009). If adaptation arose in VIP, the strongest effects should occur directly around the adaptor, but fall off the further the adaptor is removed from the test/probe (Robbins et al., 2007; Webster, 2011). In contrast, we found that adapting and probing with the same number of dots (30 in Experiment 5) did not lead to a significant motion direction-specific aftereffect (mean difference right vs. left −3.69, p=0.92, Wilcoxon signed rank test, one-sided; Bayesian posterior probability <0.18%). The presence of a strong adaptation effect when adapting with 400 and testing with 30 dots and the absence of an adaptation effect when adapting and testing with 30 dots together indicate that motion direction-numerosity cross-adaptation may arise in a human homolog of area LIP.10.7554/eLife.10806.009Figure 3.Hypothetical effect of adaptation on numerosity-encoding neurons in LIP and VIP.

Bottom Line: Do such 'recycled' circuits retain their original functionality?The reference frame of this effect is spatiotopic.Together with the tuning properties of the effect this suggests that motion direction-numerosity cross-adaptation may occur in a homolog of area LIP. 'Cortical recycling' thus expands but does not obliterate the functions originally performed by the recycled circuit, allowing for shared computations across domains.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Neural Systems, The Rockefeller University, New York, United States.

ABSTRACT
Perception of number and space are tightly intertwined. It has been proposed that this is due to 'cortical recycling', where numerosity processing takes over circuits originally processing space. Do such 'recycled' circuits retain their original functionality? Here, we investigate interactions between numerosity and motion direction, two functions that both localize to parietal cortex. We describe a new phenomenon in which visual motion direction adapts nonsymbolic numerosity perception, giving rise to a repulsive aftereffect: motion to the left adapts small numbers, leading to overestimation of numerosity, while motion to the right adapts large numbers, resulting in underestimation. The reference frame of this effect is spatiotopic. Together with the tuning properties of the effect this suggests that motion direction-numerosity cross-adaptation may occur in a homolog of area LIP. 'Cortical recycling' thus expands but does not obliterate the functions originally performed by the recycled circuit, allowing for shared computations across domains.

No MeSH data available.


Related in: MedlinePlus