An objective method for measuring face detection thresholds using the sweep steady-state visual evoked response

Abstract

We introduce a sensitive method for measuring face detection thresholds rapidly, objectively, and independently of low-level visual cues. The method is based on the swept parameter steady-state visual evoked potential (ssVEP), in which a stimulus is presented at a specific temporal frequency while parametrically varying ("sweeping") the detectability of the stimulus. Here, the visibility of a face image was increased by progressive derandomization of the phase spectra of the image in a series of equally spaced steps. Alternations between face and fully randomized images at a constant rate (3/s) elicit a robust first harmonic response at 3 Hz specific to the structure of the face. High-density EEG was recorded from 10 human adult participants, who were asked to respond with a button-press as soon as they detected a face. The majority of participants produced an evoked response at the first harmonic (3 Hz) that emerged abruptly between 30% and 35% phase-coherence of the face, which was most prominent on right occipito-temporal sites. Thresholds for face detection were estimated reliably in single participants from 15 trials, or on each of the 15 individual face trials. The ssVEP-derived thresholds correlated with the concurrently measured perceptual face detection thresholds. This first application of the sweep VEP approach to high-level vision provides a sensitive and objective method that could be used to measure and compare visual perception thresholds for various object shapes and levels of categorization in different human populations, including infants and individuals with developmental delay.

The effect of contrast polarity reversal on face detection: Evidence of perceptual asymmetry from sweep VEP

“…Stimuli were part of the set used in Ales et al (2012) and further details regarding their creation can be found in that paper. To summarise, the power spectra of a set of greyscale faces were equalised and the faces were smoothly embedded in a background composed of the phase-scrambled average power spectrum.…”

“…To determine the coherence level at which the 1F response emerged from the background EEG noise, we first estimated signal and noise with integrated response functions (see Ales et al, 2012). Signal was the cumulative sum of the amplitudes at the first harmonic (3 Hz) whereas noise was the cumulative sum of the mean noise during the trial (average amplitude of two neighbouring frequencies, 2.5 and 3.5 Hz).…”

“…2A and B). In order to quantify facerelated response, we computed an index of the 1F response (1F/ (1F + 2F), see Ales et al, 2012;Fig. 2B).…”

“…In a recent study, Ales et al (2012) used this structure-related sweep VEP to measure face detection thresholds by gradually increasing phase coherence of face images. The image stream containing faces was presented in alternation with a stream of fully phase-scrambled images at a rate of 6 Hz and face detection was indexed by periodic EEG responses at the presentation rate of face images, i.e., 3 Hz.…”

The Work of the Eye in Infant Pedagogy: A Dialogic Encounter of ‘Seeing’ in an Education and Care Setting

“…Such lingering often referred to, as 'a gaze' appears to offer important clues to researchers across multiple theoretical domains, including feminist literature (MacNaughton 1997). In recent studies of infant experience, several psychological studies compare the longer length of the gaze when newborn infants are shown human faces versus other social cues and, in doing so, make the claim that infants are more oriented to people than objects (see, for example, Ales et al 2012;Colonnesi et al 2012;Okumura et al 2013). Reddy (2012) also claims that younger infants are capable of complex eye movements based on several studies now demonstrating capacity of newborn infants to respond to facial Meltzoff 1990;Murray 2014).…”