Processing deficits for familiar and novel faces in patients with left posterior fusiform lesions

Abstract

Pure alexia (PA) arises from damage to the left posterior fusiform gyrus (pFG) and the striking reading disorder that defines this condition has meant that such patients are often cited as evidence for the specialisation of this region to processing of written words. There is, however, an alternative view that suggests this region is devoted to processing of high acuity foveal input, which is particularly salient for complex visual stimuli like letter strings. Previous reports have highlighted disrupted processing of non-linguistic visual stimuli after damage to the left pFG, both for familiar and unfamiliar objects and also for novel faces. This study explored the nature of face processing deficits in patients with left pFG damage. Identification of famous faces was found to be compromised in both expressive and receptive tasks. Discrimination of novel faces was also impaired, particularly for those that varied in terms of second-order spacing information, and this deficit was most apparent for the patients with the more severe reading deficits. Interestingly, discrimination of faces that varied in terms of feature identity was considerably better in these patients and it was performance in this condition that was related to the size of the length effects shown in reading. This finding complements functional imaging studies showing left pFG activation for faces varying only in spacing and frontal activation for faces varying only on features. These results suggest that the sequential part-based processing strategy that promotes the length effect in the reading of these patients also allows them to discriminate between faces on the basis of feature identity, but processing of second-order configural information is most compromised due to their left pFG lesion. This study supports a view in which the left pFG is specialised for processing of high acuity foveal visual information that supports processing of both words and faces.

Keywords: Face recognition; Posterior fusiform gyrus; Pure alexia; Ventral occipito-temporal cortex; Word recognition.

Fig. 1

Summary reading data for the 19 patients included in the study for (A) the reading regression slope and (B) the mean reading speed as a function of word length. Error bars indicate ± standard error. Dashed line in (A) is control mean plus 2 standard deviations.

Fig. 2

Row 1: fMRI activation during a reading task in 15 normal subjects (words – checkerboards, p < .05; FDR) Row 2: lesion overlap maps for all 17 patients included in the study with scans; Row 3: lesion overlap maps for the eight patients with the mildest reading impairment; Row 4: lesion overlap maps for the nine patients with the most severe impairment; and Row 5: Lesion map for patient 125, with a severe reading impairment, showing a small lesion confined to the left fusiform gyrus/occipito-temporal sulcus. .The axial slices of the MNI template brain in MRIcron have been rotated −15° from the AC-PC line in order to display the entire posterior-anterior course of the fusiform gyrus.

Fig. 3

Functional Acuity Contrast Test results for eight of the nine UK patients in the current study. Grey lines represent normal range.

Fig. 4

Means reaction times and accuracy for nine patients and nine matched controls for the famous face (A) naming (patient accuracy range = 15–93%) and (B) matching (patient accuracy range = 63–100%). Error bars indicate ± standard error.

Fig. 5

Examples for same and different stimuli for each condition of the Jane Faces task.

Fig. 6

Performance for conditions of the face discrimination task for the patient subgroups split by severity (slope of the length effect in RT) and controls. Error bars represent standard error.