RESEARCH I REPORT Fig.2.TP is es TP AM st -02 (e)) 0 C)TP(left)adAM(ie） 000 popu AM ()) 102 MDS1(12%) MDS113%) 3 21 160185 char TP pop 5 nihar),and gray b ground (5 images) upp rate t on An e ample cel from area ID,let) )re ded similarly to lation response 2 ot,clustered togethe ig. Dand resp onsive to nonface stimuli and E 2431799,p<10 s was higher for AM is ability inde selectively to the faces several familiar ty o =057±0.01]than TP(S =0.26± d sivenes and stimulus ategories [three ay Anova inter nonkey fam iiar face clus was highe whole (Fig.2A and fig y x cate responde there wer ignificant fam effect is fun me nce betwe TP and ods)and the TP population prefe rred monke sults (Fig 2F)Crueially TP's familiarit d not result f m passive visua wo-way analy The pattern of the TP tion r of times-but rather from real-life persona F21s24■8 so spec ed fo amiliar a different (HSD)test:p Selectivity for monkey faces (Fig2D,left)and were adjacent mod ace Landi et al,&aine373,581-585(202） 30Juy202 2of51 subject’s own face, 72 unfamiliar), bodies (15 unfamiliar), objects (15 personally familiar, 25 unfamiliar), and gray background (5 images) (face object familiarity, FOF image set). An example cell from area TP (Fig. 1D, left) remained visually unresponsive to any of the 145 face stimuli, with one exception—the face of a personally familiar monkey (stimulus 33). Another example cell (Fig. 1D, right) was un￾responsive to nonface stimuli and responded selectively to the faces of several familiar monkeys. This pattern of high visual respon￾siveness, preference for monkey faces, and selectivity for familiar faces was typical for the TP population as a whole (Fig. 2A and fig. S2): Ninety out of 98 (92%) neurons responded significantly to at least one image (see meth￾ods), and the TP population preferred monkey over human faces and familiar over unfamiliar monkey faces [Fig. 2, A and C, left; significant two-way analysis of variance (ANOVA) stimu￾lus category x familiarity: F2,18124 = 89.61, p < 10−39; post hoc Tukey’s honestly significantly different (HSD) test: p < 10−4 ]. Selectivity for face familiarity was so high that the TP pop￾ulation responded more than three times as much to familiar than to unfamiliar monkey faces. AM cells, though also visually responsive (125 of 130, 96%), responded similarly to both monkey and human faces and familiar and unfamiliar faces [Fig. 2, B and C, and figs. S1B and S2; interaction effects F2,24044 = 2.22, p > 0.1; familiarity effect F1,24044 = 0.3, p > 0.1; stimulus category F2,24044 = 317.99, p < 10−100]. The effect of familiarity on neuronal responses differed between TP and AM and between stimulus categories [three-way ANOVA inter￾action effect area x familiarity x category, F2,42168 = 31.29, p < 0.001]. Whereas in AM there were no significant familiarity effects for any category (p > 0.1), in TP, familiar monkey faces elicited a significantly higher response than all other categories (post hoc tests, p < 10−4 corrected using Tukey’s HSD). The pattern of the TP population response was also specialized for familiar faces: Popu￾lation responses were most similar for familiar monkey faces (Fig. 2D, left) and were adjacent and separate from unfamiliar monkey faces in a two-dimensional representational space (Fig. 2E, left), supporting accurate decoding of only the familiar monkey category (Fig. 2F, left; see methods). In AM, population response similar￾ity was high for all categories, and stimuli belonging to the same category, whether fa￾miliar or not, clustered together (Fig. 2, D and E, right). Although the separability of faces and objects was higher for AM [separability index (SI) = 0.57 ± 0.01] than TP (SI = 0.26 ± 0.01, permutation test p < 0.005), the separability of a monkey familiar face cluster was higher in TP (SI = 0.73 ± 0.02; see methods) than in AM (SI = 0.43 ± 0.03, permutation test p < 0.005). This fundamental difference between TP and AM was also reflected in category decoding results (Fig. 2F). Crucially, TP’s familiarity selectivity did not result from passive visual exposure—subjects saw all pictures thousands of times—but rather from real-life personal encounters. TP cells express one key property of face recognition units (3): modulation by face Landi et al., Science 373, 581–585 (2021) 30 July 2021 2 of 5 Fig. 2. TP is selective for familiar monkey faces but not other familiar stimuli. (A) Population response matrices (z-scored, color scale lower right) to FOF stimulus set (top) for all recorded TP cells (n = 98, sorted top to bottom by face selectivity index; see methods). The average population response (mean z score ± SEM) is shown at the bottom. (B) Same as (A) for AM (n = 130). (C) TP (left) and AM (right) population response (average z scores, error bars indicate 95% confidence intervals) for six catego￾ries [color scales as in (A)]. Significant post hoc tests (***p < 10−4 , corrected using Tukey’s HSD) are shown for familiar versus unfamiliar stimuli. (D) TP (left) and AM (right) popula￾tion response dissimilarity matrix showing the dissimilarity (D) between all pairs of FOF stimuli quantified as 1 − Pearson correlation coefficient; color scale is shown at the lower right. (E) Individual stimuli in two-dimensional space derived from the multidimensional scaling (MDS) of dissimilarity. The explained variance is shown for each dimension in the axis labels. (F) TP (left) and AM (right) population category decoding performance measured by linear classifier performance (see methods). Classification Accuracy (%) 0 50 100 chance F E 20 40 60 80 100 120 -2 0 2 4 1 30 43 98 160 185 58 Stimulus index E 20 30 40 50 60 70 80 90 Cell number zScore 10 -2 0 2 4 Familiar Unfamiliar 0.4 1 D D -10 10 0 AM A TP C TP B Cell number zScore -2 0 2 0 2 MDS 1 (12%) MDS 2 (5%) MDS 1 (13%) 0 3 0 2 MDS 2 (8%) -0.2 0.2 0.6 1 1.4 zScore Human Monkey Objects *** Human Monkey Objects -0.2 0.2 0.6 1 1.4 zScore -10 10 0 AM 0.4 1 D Classification Accuracy (%) 0 50 100 chance RESEARCH | REPORT Downloaded from https://www.science.org at Southern Medical University on May 08, 2022