All-or-none visual categorization in the human brain

Abstract

Whether visual categorization, i.e., specific responses to a certain class of visual events across a wide range of exemplars, is graded or all-or-none in the human brain is largely unknown. We address this issue with an original frequency-sweep paradigm probing the evolution of responses between the minimum and optimal presentation times required to elicit both neural and behavioral face categorization responses. In a first experiment, widely variable natural images of nonface objects are progressively swept from 120 to 3 Hz (8.33 to 333 ms duration) in rapid serial visual presentation sequences; variable face exemplars appear every 1 s, enabling an implicit frequency-tagged face-categorization electroencephalographic (EEG) response at 1 Hz. In a second experiment, faces appear non-periodically throughout such sequences at fixed presentation rates, while participants explicitly categorize faces. Face-categorization activity emerges with stimulus durations as brief as 17 ms for both neural and behavioral measures (17 – 83 ms across individual participants neurally; 33 ms at the group level). The face-categorization response amplitude increases until 83 ms stimulus duration (12 Hz), implying graded categorization responses. However, a strong correlation with behavioral accuracy suggests instead that dilution from missed categorizations, rather than a decreased response to each face stimulus, may be responsible. This is supported in the second experiment by the absence of neural responses to behaviorally uncategorized faces, and equivalent amplitudes of isolated neural responses to only behaviorally categorized faces across presentation rates, consistent with the otherwise stable spatio-temporal signatures of face-categorization responses in both experiments. Overall, these observations provide original evidence that visual categorization of faces, while being widely variable across human observers, occurs in an all-or-none fashion in the human brain.

The Relationship Between the Benton Face Recognition Test and Electrophysiological Unfamiliar Face Individuation Response as Revealed by Fast Periodic Stimulation

“…One reason for that is that time pressure in explicit unfamiliar face discrimination tasks can deteriorate behavioral performance even in healthy adult participants (Bindemann, Fysh, Cross, & Watts, 2016; Fysh & Bindemann, 2017) and could even be more problematic (or impossible to apply) when testing children or clinical populations. Future studies with neurotypical adults could examine if varying the presentation rate of the stimulus could increase the correlation of performance in these conditions with EEG measures of face individuation with FPVS (see, e.g., Retter, Jiang, Webster, & Rossion, 2019 for such an approach used with generic face categorization).…”

Varying Stimulus Duration Reveals Consistent Neural Activity and Behavior for Human Face Individuation

“…While other stimulus features were not standardized across facial identities (width, luminance, contrast, color, etc. ), these aspects were modulated at every stimulus presentation, in order to increase their variability for each identity and thus reduce their diagnosticity across different identities (i.e., low-level stimulus control by variability, e.g., Thorpe, Fize & Marlot, 1996;Crouzet et al, 2010;Foldiak et al, 2004;Rossion et al, 2015;Retter et al, 2020). At every presentation, the stimulus size varied randomly from 80 to 120% of the original size (sampled in 5% steps; see Dzhelyova & Rossion, 2014), and the luminance varied randomly from -10 to +10% of the original (sampled in 2.5% steps).…”

“…This experiment was based on a novel combination of two recently established EEG frequencytagging approaches: 1) an oddball paradigm to measure high-level face individuation (FI; since Liu-Shuang et al, 2014;reviewed in Rossion, Retter & Liu-Shuang, 2020); and 2) a frequencysweep design (Retter et al, 2020). In the oddball paradigm, one facial identity is repeated as the "base" face, while randomly selected "oddball" faces are interleaved at a fixed interval, i.e., as every n th stimulus.…”

“…In the frequency-sweep design, F is continuously swept through descending frequency rates within each testing sequence (e.g., from 40 to 30 to 20 Hz (i.e., 25 to 33 to 50 ms), etc. ), while F/n remains constant at 1 Hz (1 s; Retter et al, 2020). This design was created to measure the first, shortest duration (i.e., highest frequency) at which the differential F/n response would appear, as well as to characterize F/n (relative to F) responses across stimulus presentation rates.…”

“…Here, we address this question by investigating the impact of stimulus duration on FI, both behaviorally and neurally, with a focus on relating inter-individual differences at both measures. We used a novel combination of an oddball paradigm for measuring robust, highlevel neural FI responses, even at the individual participant level (from Liu-Shuang et al, 2014;review: Rossion, Retter & Liu-Shuang, 2020) and a frequency-sweep design for progressively increasing stimulus duration within each stimulation sequence, in 11 steps from 25 to 333 ms (40 to 3 Hz), with forward-and backward-masking deriving from a 0 ms inter-stimulus-interval (from Retter et al, 2020;see Methods). We define the minimal stimulus duration for FI (i.e., the smallest stimulus duration to elicit a significant response), with convergent results produced for neural and behavioral measures, as well as the optimal stimulus duration (i.e., the smallest stimulus duration generating the largest response).…”