Unconscious categorization of sub-millisecond complex images

Abstract

Can people categorize complex visual scenes unconsciously? The possibility of unconscious perception remains controversial. Here, we addressed this question using psychophysical methods applied to unmasked visual stimuli presented for extremely short durations (in the μsec range) by means of a custom-built modern tachistoscope. Our experiment was composed of two phases. In the first phase, natural or urban scenes were either absent or present (for varying durations) on the tachistoscope screen, and participants were simply asked to evaluate their subjective perception using a 3-points scale (absence of stimulus, stimulus detection or stimulus identification). Participants' responses were tracked by means of two staircases. The first psychometric function aimed at defining participants' proportion of subjective detection responses (i.e., not having seen anything vs. having seen something without being able to identify it), while the second staircase tracked the proportion of subjective identification rates (i.e., being unaware of the stimulus' category vs. being aware of it). In the second phase, the same participants performed an objective categorization task in which they had to decide, on each trial, whether the image was a natural vs. an urban scene. A third staircase was used in this phase so as to build a psychometric curve reflecting the objective categorization performance of each participant. In this second phase, participants also rated their subjective perception of each stimulus on every trial, exactly as in the first phase of the experiment. Our main result is that objective categorization performance, here assumed to reflect the contribution of both conscious and unconscious trials, cannot be explained based exclusively on conscious trials. This clearly suggests that the categorization of complex visual scenes is possible even when participants report being unable to consciously perceive the contents of the stimulus.

Dyslexic Readers Improve without Training When Using a Computer-Guided Reading Strategy

“…If a subject who is only able to recognize 3 letters simultaneously tries to recognize 6 letters simultaneously s/he will make reading mistakes: S/he will swap letters, displace letters, omit letters, and read letters that do not occur in the word. The finding that recognition depends on the presentation time of stimuli is in agreement with psychophysical [73][74][75][76][77][78][79] and neurobiological studies [80] and earlier studies on the recognition of pseudowords [37][38][39]. Temporal summation explains both the improvement in recognizing a sequence of letters with increased fixation time [37][38][39] and poor readers' prolonged fixation times reported in previous studies [81][82][83][84][85].…”

“…In Experiment 1 the presentation time was limited to 500 ms, because temporal summation is effective up to this fixation time [ 73 ]. The results of Experiment 1 and earlier studies on temporal summation [ 37 , 38 , 39 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ] support the hypothesis that improvement of word recognition requires prolongation instead of shortening [ 32 , 86 , 87 , 88 ] of the fixation time. The finding that readers improve when they extend their fixation times demonstrates that attention does not decrease during fixation, and that the readers can maintain their attention for the required fixation time.…”

“…Therefore, reduced ability to simultaneously recognize all letters in a pseudoword should not be regarded as a consequence of an impaired visual attention span [ 61 , 62 , 65 , 66 , 95 , 96 , 97 , 98 ]. Many poor readers improved their ability to simultaneously recognize a string of letters by applying a longer fixation time, i.e., an increased temporal summation [ 73 , 74 , 75 , 76 , 77 , 78 , 79 ]. Nineteen children were unable to recognize pseudowords consisting of 4 or 5 letters even if the fixation time was prolonged up to 500 ms.…”

Is Developmental Dyslexia Due to a Visual and Not a Phonological Impairment?

“…First column on the left: fixation times of pseudowords; second column: number of subjects who were able to read 3-letter pseudowords within fixation times between 250 and 500 ms; third column: number of subjects who were able to read 4-letter pseudowords within fixation times between 250 and 500 ms; fourth column: number of subjects who were able to read 5-letter pseudowords within fixation times between 250 and 500 ms. Fifth column: number of subjects who were able to read 6-letter pseudowords within fixation times between 250 and 500 ms. The improvement in the ability to recognize pseudowords simultaneously when the fixation time is prolonged is due to temporal summation [152][153][154][155][156][157][158][159][160][161][162][163][164][165]. Detection and recognition of visual stimuli [152][153][154][155][156][157][158][159], and visual acuity improve when fixation time increases [160][161][162][163][164][165].…”

An academic survey on theoretical foundations, common assumptions and the current state of consciousness science

“…It seems that the general assumption in the field is that virtually all cognitive functions can happen unconsciously because even for the two 'highest' cognitive functions, thinking and meta-cognition, the 'yes' responses and 'no' responses were equally divided, despite scarce empirical evidence. Thus, even though several methodological caveats have been identified over the years in the study of unconscious cognition (Meyen et al, 2021;Newell & Shanks, 2014;Schmidt & Vorberg, 2006;Shanks, 2017), and the depth and scope of unconscious processes is debated (Beauny et al, 2020;Dehaene & Naccache, 2001;Hassin, 2013;Kunde et al, 2012;Meyen et al, 2021;Newell & Shanks, 2014;Van Gaal & Lamme, 2012), it seems that at present the community is convinced about the existence of extensive unconscious processing the brain.…”