The influence of intrinsic and extrinsic grouping cues on numerosity perception of groupitizing: Evidence from fMRI

doi:10.3724/SP.J.1041.2026.0323

Abstract

Abstract:

This study employed a numerosity estimation task combined with fMRI technology to investigate the effects of intrinsic and extrinsic grouping cues on groupitizing strategies in numerosity perception and to reveal the neural mechanisms underlying these strategies. The results showed that grouped conditions elicited stronger activation in calculation-related brain regions such as the left intraparietal sulcus (IPS), angular gyrus (AG), and superior frontal gyrus (SFG) compared to ungrouped conditions. Extrinsic grouping cues elicited stronger activation in brain regions associated with topological properties, such as the middle frontal gyrus (MFG) and inferior temporal gyrus (ITG), compared to intrinsic grouping cues. The findings indicate that participants were more inclined to use calculation-related strategies for numerosity perception under grouped conditions, and that extrinsic grouping cues possess topological properties, supporting the theory of topological perception.

Key words: numerosity perception, groupitizing strategy, grouping cues, theory of topological perception, functional magnetic resonance imaging (fMRI)

PAN Yun, YANG Huanyu, JIA Liangzhi, ZHU Jun, YU Fangwen, ZHANG Di, YANG Ping. (2026). The influence of intrinsic and extrinsic grouping cues on numerosity perception of groupitizing: Evidence from fMRI. Acta Psychologica Sinica, 58(2), 323-335.

Figures/Tables 12

Figure 1. Examples of Stimulus Materials. A-C: Distribution diagrams for common region, connectedness, and proximity stimuli; D-G: Schematic diagrams of extrinsic and intrinsic grouping cue stimuli. For all cues, the left side shows the grouped condition and the right side the ungrouped condition (for clarity, stimuli are not drawn to scale in the figure). Color versions are available in the electronic edition. The same applies below.

Figure 2. Experimental Procedure Flowchart.

Figure 3. Perceptual Accuracy (A) and Reaction Time (B) Results for Condition and Grouping Cue.
Note. ^*** p < 0.001, ^**p < 0.01, ^* p < 0.05, ns not significant. Error bars represent standard error of the mean.

Figure 4. Activated brain regions and differential brain regions for the grouped and ungrouped conditions.

Table 1 Brain regions activated in the grouped and ungrouped conditions from whole-brain analysis

Activated Brain Regions	Hemisphere	Number of Voxels	MNI			t
Activated Brain Regions	Hemisphere	Number of Voxels	x	y	z	t
grouped conditions
IPS/AG/SMG	Left	707	-30	-55	42	5.76
ITG/LG	Left	408	-51	-58	-10	5.64
MFG	Left	173	-51	8	32	5.50
IPS	Right	154	21	-58	42	5.76
ungrouped conditions
IPS/AG	Right	128	30	-61	54	4.53
IPS/AG/SPL	Left	79	-33	-55	52	4.26
SMG	Left	40	-45	-22	52	5.26
MFG	Left	34	-45	5	32	3.98
LG	Right	33	9	-88	-6	4.38
SMA	Right	24	-6	5	56	4.18

Table 2 Differential brain activation for Grouped Condition > Ungrouped Condition

Activated Brain Regions	Hemisphere	Number of Voxels	MNI			t
Activated Brain Regions	Hemisphere	Number of Voxels	x	y	z	t
IPS/AG	Left	185	-36	-52	54	6.40
ITG	Left	163	-42	-58	-14	6.14
SMG/AG	Right	87	57	-40	30	4.79
SMG	Left	48	-51	-40	40	4.67
LG	Right	38	3	-61	-8	6.03

Figure 5. Activated brain regions and differential brain regions for extrinsic and intrinsic grouping cues.

Table 3 Brain regions activated for extrinsic and intrinsic grouping cues from whole-brain analysis

Activated Brain Regions	Hemisphere	Number of Voxels	MNI			t
Activated Brain Regions	Hemisphere	Number of Voxels	x	y	z	t
Extrinsic grouping cues
MFG/LG	Right	2297	24	-58	42	6.30
IPS/AG/SMG/ITG	Left	1489	-21	-50	40	6.12
MFG	Left	510	-45	5	30	6.05
Postcentral gyrus	Left	247	48	5	32	5.39
SMA	Left	192	-6	8	54	5.10
INS/SPL	Right	124	33	20	6	5.65
Intrinsic grouping cues
IPS/SMG/AG	Left	345	-36	-37	36	5.83
IPS/AG/SMG	Right	267	36	-55	50	6.56
INS	Left	170	-27	14	14	4.80
MFG/SMG	Left	134	-45	-1	32	4.83
SMA	Left	120	-6	-1	56	4.79

Table 4 Differential brain activation for extrinsic grouping cues > intrinsic grouping cues

Activated Brain Regions	Hemisphere	Number of Voxels	MNI			t
Activated Brain Regions	Hemisphere	Number of Voxels	x	y	z	t
SMA/MFG/IPS	Left	1037	-30	44	38	5.76
ITG	Left	233	-53	-23	-18	5.86
ITG	Right	221	45	-31	-8	5.94
LG	Left	59	-12	-85	-16	5.64

Table 5 Functional connectivity where the grouped condition is stronger than the ungrouped condition, with the left IPS as the seed point.

Seed	Region	Number of Voxels	MNI			t
Seed	Region	Number of Voxels	x	y	z	t
Left-IPS	Right-IPS	265	30	-69	36	5.85
	Right-AG	56	42	-55	18	5.32
	Right-SFG	102	33	50	11	5.28
	Left-IPS	89	-36	-58	50	6.99

Figure 6. A: gPPI analysis results for the grouped condition minus the ungrouped condition, with the left IPS as the seed point; B: gPPI analysis results for the external grouping cue minus the internal grouping cue, with the left ITG as the seed point.

Table 6 Functional connectivity where the external grouping cue is stronger than the internal grouping cue, with the L-ITG as the seed point.

Seed	Region	Number of Voxels	MNI			t
Seed	Region	Number of Voxels	x	y	z	t
Left-ITG	Left-IPS	132	-33	-65	32	6.35
	Left-LG	169	-42	-45	18	8.52
	Left-SFG	256	-36	43	10	5.32
	Left-ITG	152	-52	-64	-18	6.35
	Right-ITG	53	54	-58	-14	5.65

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