Electrophysiological markers of covert face recognition in developmental prosopagnosia

Abstract

To study the existence and neural basis of covert face recognition in individuals with developmental prosopagnosia, we tested a group of 12 participants with developmental prosopagnosia in a task that required them to judge the familiarity of successively presented famous or non-famous faces. Electroencephalography was recorded during task performance, and event-related brain potentials were computed for recognized famous faces, non-recognized famous faces and non-famous faces. In six individuals with developmental prosopagnosia, non-recognized famous faces triggered an occipito-temporal N250 component, which is thought to reflect the activation of stored visual memory traces of known individual faces. In contrast to the N250, the P600f component, which is linked to late semantic stages of face identity processing, was not triggered by non-recognized famous faces. Event-related potential correlates of explicit face recognition obtained on those few trials where participants with developmental prosopagnosia classified famous faces as known or familiar, were similar to the effects previously found in participants with intact face recognition abilities, suggesting that face recognition mechanisms in individuals with developmental prosopagnosia are not qualitatively different from that of unimpaired individuals. Overall, these event-related potential results provide the first neurophysiological evidence for covert face recognition in developmental prosopagnosia, and suggest this phenomenon results from disconnected links between intact identity-specific visual memory traces and later semantic face processing stages. They also imply that the activation of stored visual representations of familiar faces is not sufficient for conscious explicit face recognition.

The activation of visual face memory and explicit face recognition are delayed in developmental prosopagnosia

“…The N250 to participants' own face was already present in the first half of the experiment, while the N250 to target faces only emerged during the second half, suggesting that an episodic representation of a previously unfamiliar target face builds up gradually (see also Kaufmann, Schweinberger, & Burton, 2009). Target Faces and Own faces also elicited a sustained positivity that peaked around 500 ms post-stimulus in the study by studies of famous face recognition (Gosling & Eimer, 2011;Eimer et al, 2012).…”

“…The P600f has been linked to the attentional processing and the explicit recognition of individual task-relevant faces, as well as to the retrieval of semantic or episodic information about these faces (e.g., Tanaka et al, 2006;Gosling & Eimer, 2011;Eimer et al, 2012). Because the Target Face "Joe" was pre-experimentally unfamiliar, the P600f component triggered by this face is unlikely to be linked to an activation of semantic or episodic memory, and should thus primarily reflect focal-attentional processing and explicit face recognition.…”

The Cognitive and Neural Basis of Developmental Prosopagnosia

“…While the ERP study by Eimer et al (2012) investigated the recognition of famous faces, which are likely to be represented in long-term memory, a recent experiment (Parketny, Towler, & Eimer, 2015) studied the processes that are responsible for the recognition of previously unfamiliar but now task-relevant faces in DP. In an experimental paradigm developed by Tanaka et al (2006), single face images were presented sequentially, and participants had to respond to a previously studied but otherwise unknown target face ("Joe"), while ignoring other task-irrelevant distractor faces.…”

Face identity matching is selectively impaired in developmental prosopagnosia

“…Based on this distribution, the reliability of an empirically observed ERP difference between conditions was determined for individual participants. If the probability of obtaining the observed difference by chance is below 5%, it can be accepted as statistically significant (see Dalrymple et al, 2011;Eimer, et al 2012;Oruc et al, 2011;Fisher et al, 2016b, for previous applications of this procedure in ERP studies of prosopagnosia). In the present experiment, this bootstrap procedure was based on EEG mean amplitudes obtained between 220 and 320 ms after S2 onset on identity repetition and identity change trials where facial expression was repeated (collapsed the eight lateral posterior electrodes over the left and right hemisphere).…”