Criterion Shifts and the Metaphysics of Sensory Experience

Authors

Assaf Weksler

Affiliation: Ben Gurion University of the Negev

Category: Philosophy

Keywords: Philosophy of perception, Signal detection theory, Phenomenal externalism, Externalist representationalism, Criterion shifts

Schedule & Location

Date: Tuesday 2nd of September

Time: 16:00

Location: Gen. Henryk Dąbrowski Hall (006) 📍

View the full session: Metaphysics of Perceptual Experience

Abstract

In this talk I build a bridge between a debate in the scientific study of consciousness, about criterion shifts, and a debate in the metaphysics of conscious experience, about phenomenal externalism vs. internalism.

Signal Detection Theory (SDT) studies (Green & Swets, 1966; Macmillan & Creelman, 2005) have found that, in detection tasks, participants answer ‘stimulus present’ if and only if the sensory response intensity surpasses their pre-set detection criterion. The matter is typically depicted via two partially overlapping curves, representing the probability distributions of internal response intensity for the two conditions, namely ‘stimulus absent’, and ‘stimulus present’. When base-rate and payoff are neutral, putting the criterion at the intersection of the curves (see Figure 1) is optimal, since it maximizes hits (reporting ‘present’ when the stimulus is present) and correct rejections (reporting ‘absent’ when the stimulus is absent). Although false alarms (reporting ‘present’ when the stimulus is absent) and misses (reporting ‘absent’ when the stimulus is present) still occur, they are jointly minimized to the greatest extent possible. The miss area and hit area, in Figure 1, reflect the miss rate and the hit rate, respectively. The hit rate is much larger than the miss rate. Analogously, the correct rejection rate is much larger than the false alarm rate.

Figure 1. The probability distributions (probability density functions) for the stimulus absent and stimulus present conditions, in a representative detection task, including depiction of miss and hit rate, via miss and hit areas, respectively. The units of sensory response intensity are arbitrary.

The criterion shifts when payoff and base-rate are manipulated (Macmillan & Creelman, 2005). For example, if misses are penalized by 5 Euros while false alarms are penalized by 1 Euro, participants adopt a liberal criterion, so they report ‘stimulus present’ more often, thus reducing misses—and increasing false alarms—which increases expected utility. There are also suboptimal criterion shifts. For example, stimuli in the visual periphery are over-reported due to a use of a liberal detection criterion, regardless of payoff or base-rate (Solovey et al., 2015).

There are two different interpretations of criterion shift effects. According to Experiential Criterion, the sensory response intensity is intensity of unconscious neuronal activity. If it surpasses the criterion, an experience is formed. So, shifting the criterion to the liberal side means having more experiences. According to Post Experiential Criterion, in contrast, sensory response intensity is the intensity of a conscious experience. If it surpasses the criterion, a 'stimulus present' report is formed. So shifting the criterion to the liberal side means increasing 'stimulus present' reports, without any change to experiences.

The interpretation of criterion shifts has significant implications for topics such as the richness of phenomenology (Abid, 2019; Brown, 2024; Knotts et al., 2020; Solovey et al., 2015), blindsight (Ko & Lau, 2012; Michel & Lau, 2021; Phillips, 2021), scientific theories of consciousness (Lau, 2022), and top-down influence of belief and desire on perception (Sánchez-Fuenzalida et al., 2022). So far, the evidence presented in the debate has been empirical (including philosophical analysis of empirical findings). In the paper on which this talk is based, I argue that Phenomenal Externalism—the metaphysical view that an experience as of an F is constituted by a brain state that bears some physical-functional relation to external items—conflicts with Post-Experiential Criterion. Phenomenal externalism—as I am using the term—includes externalist representationalism (Byrne & Tye, 2006; Cutter, 2016; Cutter & Tye, 2011; Dalbey & Saad, 2022; Dretske, 1997; Lycan, 2021; Saad, 2024; Tye, 1997) as well as Schellenberg's Capacitism (2018). Given the limited time available for this talk, I will concentrate on a specific version of phenomenal externalism. This version is teleological: according to it, an experience as of F is constituted by a brain state (call it N) whose (unique) function is to respond to Fs (Dretske, 1997). (On Schellenberg's Capacitism, the experience is constituted by the employment of a capacity whose function is to discriminate and single out Fs. My argument straightforwardly applies to that view as well). Moreover, the version I focus on relies on the non-etiological, biostatistical account of function developed by Garson & Piccinini (2014). Very roughly, on that approach, a function of E is to φ iff the typical contribution of E to survival or inclusive fitness occurs through φ-ing.

The argument, in a nutshell, is as follows. Focus (without loss of generality) on sensory response with intensity 3, and assume (also without loss of generality) a neutral criterion as in Figure 1. According to Post-Experiential Criterion, the sensory response is an experience with intensity '3' (an experience as of a faint stimulus). Because it is below the criterion (set on 3.5), the subject reports 'stimulus absent'. So, this experience contributes to survival or inclusive fitness (when it does) through producing correct rejections. Let N be the brain state that constitutes this experience. Thus, producing correct rejections in a detection task is a typical contribution to survival or inclusive fitness by N. So, a function of N is to respond to the absence of a stimulus. But on teleological phenomenal externalism, the unique function of N is to respond to the presence of a (faint) stimulus. We reached a contradiction. Thus Post Experiential Criterion is incompatible with Teleological Phenomenal Externalism.

The argument leads to the construction of a new “bridge” linking the metaphysics of sensory experience with the scientific study of consciousness. It is possible to walk over the bridge in both directions, i.e., to use Teleological Phenomenal Externalism against the post-experiential interpretation of criterion shifts, or vice versa. If the scientific debate about criterion shifts is difficult to settle, the bridge suggests looking for answers in metaphysics. If the debate can be settled, independently of metaphysics, in favor of Post Experiential Criterion, this will knock over Teleological Phenomenal Externalism.

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