Wednesday, February 25, 2009

Linguistic effects on unconscious color perception

The post headline may seem an oxymoron , but it is indeed possible to perceive colors unconsciously. How do we know that someone has perceived a color, when he doesn't report the qualia. We do so by measuring the effects on subsequent behavior. Consider subliminal priming. Consider a subliminal stroop test, in which color patches are presented subliminally and then color lexical terms are presented consciously in neutral (say black) ink. I'm sure with this subliminal modified stroop test one could still get a color and lexical term interaction effect; the point is that color , when not perceived, may still influence subsequent behavior.

The experimental paradigm in this PNAS article did not go so far, but restricted itself to color stimuli that was not attended to; that is, the color was indeed perceived, but it was not attended to (the task involved attention to form rather than color) and so as the color was not attended to, they presumed that the effects that the color information would have on behavior would be completely unconscious. I'm not convinced, but that doesn't invalidate their otherwise very beautiful study that once again provides strong evidence for the milder version of the Sapir-Whorf hypothesis, at least as it relates to categorical color perception. 

Now, I have written previously about Sapir- Whorf hypothesis in general,  and in particular about the ability of Russians( who have two separate terms for light and dark blue) to visually discriminate between light and dark blue significantly better than their English counterparts, thanks to their rich color lexicon; so this new study that found that Greek-natives (who also have different lexical terms for light and dark blue) were superior to English-natives in terms of discriminating categorical color perception for light and dark blue color, did not come as a surprise or seemed ground-breaking; but there are important differences both in terms of the procedures used and the processes involved.

This study, works at pre-attentive level, uses physiological measures like ERP (they studied the vMMN - visual Mismatch Negativity) to determine whether the color stimuli had differential effect even at pre-attentive perception and thus provides independent evidence for the effect of Language on color perception. I'll now quote from the abstract and discussion section:

It is now established that native language affects one’s perception of the world. However, it is unknown whether this effect is merely driven by conscious, language-based evaluation of the environment or whether it reflects fundamental differences in perceptual processing between individuals speaking different languages. Using brain potentials, we demonstrate that the existence in Greek of 2 color terms—ghalazio and ble—distinguishing light and dark blue leads to greater and faster perceptual discrimination of these colors in native speakers of Greek than in native speakers of English. The visual mismatch negativity, an index of automatic and preattentive change detection, was similar for blue and green deviant stimuli during a color oddball detection task in English participants, but it was significantly larger for blue than green deviant stimuli in native speakers of Greek. These findings establish an implicit effect of language-specific terminology on human color perception.

This study tested potential effects of color terminology in different languages on early stages of visual perception using the vMMN, an electrophysiological index of perceptual deviancy detection. The vMMN findings show a greater distinction between different shades of blue than different shades of green in Greek participants, whereas English speakers show no such distinction. To our knowledge, this is the first demonstration of a relationship between native language and unconscious, preattentive color discrimination rather than simply conscious, overt color categorization.

To conclude, our electrophysiological findings reveal not only an effect of the native language on implicit color discrimination as indexed by preattentive change detection but even electrophysiological differences occurring as early as 100 ms after stimulus presentation, a time range associated with activity in the primary and secondary visual cortices (22). We therefore demonstrate that language-specific distinctions between 2 colors affect early visual processing, even when color is task irrelevant. At debriefing, none of the participants highlighted the critical stimulus dimension tested (luminance) or reported verbalizing the colors presented to them. The findings of the present study establish that early stages of color perception are unconsciously affected by the terminology specific to the native language. They lend strong support to the Whorfian hypothesis by demonstrating, for the first time, differences between speakers of different languages in early stages of color perception beyond the observation of high-level categorization and discrimination effects strategically and overtly contingent on language specific

I think this fits in with predictive models of perception, wherein, earlier stages of visual processing, that are unrelated to color discrimination, may still be primed by color information that one has obtained earlier and has processed pre-attentively. I, as always , am excited by this proof of whorfian hypotheses.

Sphere: Related Content

1 comment:

Podblack said...

Hi! All entered for the #65th Encephalon - this was a great read, thanks!