Does radial bias influence fast saccades toward faces in the periphery?

Saccadic choice studies showed that humans initiate the fastest saccades towards faces compared to other visual categories such as animals, objects and scenes. These studies typically present images peripherally, along the horizontal meridian (HM). Our past work showed that face-specialized mechanisms engage most strongly along the HM due to the radial bias facilitating access to the horizontal structure of the face, known to optimally drive face detection and identification. We therefore hypothesized the set-up of past saccadic choice studies may have privileged the access to the horizontal structure of the human face, and therefore (partly) account for the saccadic advantage for faces reported so far. Fifty participants performed a saccadic choice task with stimuli presented at 15° eccentricity along both the horizontal (HM) and vertical meridians (VM). We examined the influence of meridian orientation on the saccadic advantage for faces, considering the role of radial bias. In addition, we assessed the horizontal tuning of face-specialized processing using a face identity recognition task, and measured contrast sensitivity along the HM and VM to evaluate radial bias strength. Our findings showed that saccades toward faces were faster and more accurate than those toward vehicles, even along the VM. We found a significant relationship between radial bias strength and faster saccades toward faces along the HM. Additionally, a stronger horizontal tuning for face identity recognition was associated with a greater face advantage along the VM. These results indicate that radial bias and horizontal tuning independently contribute to ultra-fast saccades toward faces in the periphery.