The FOF Machinery

These reflections on the FOK and TOT foreshadow the mechanisms behind the FOF.

The dominant account of the FOF is largely analogous to the processing fluency account of the FOK, proposing perceptual fluency as an initial recognition signal. The idea is that a previous encounter with a stimulus will facilitate its perceptual processing upon a renewed encounter, resulting in perceptual fluency. This fluency, in turn, will be attributed to the stimulus being familiar, triggering a FOF.

The ability to perceive and process something quickly and easily is evidence that the cognitive system has processed the stimulus in the past. It is the at-tribution of processing fluency to prior exposure that gives rise to familiarity (Verde et al. 2010, p. 142).

5.3.2.1. Main Exhibit 5: Discrepant Processing Fluency

One interesting extension that work on the FOF has brought to the fore is that fluency cannot only pertain to different processes but that the fluency pertaining to a specific process can take different forms. Specifically, it has become apparent that the effects of objective fluency, as well as the phenomenology of fluency-based epistemic feelings, tend to be more pronounced and salient if a process is not only fluent butdiscrepantly fluent, i.e. if a process is not “just fast” (absolute fluency) but fast relative to something else (relative fluency) (Whittlesea and Leboe 2003, see also section 5.2).¹⁵³ A process can be discrepantly fluent in several complementary ways: It can be discrepantly fluent relative to 1) the rest of the currently ongoing processing background, i.e. a specific process can be fast and therefore fluent relative to other ongoing processes, or 2) relative to an expectation concerning the speed of the specific processing, whereas this expectation is formed 2.1) outside or 2.2) within the present context (Whittlesea and Leboe 2003;

Hansen and W¨anke 2013; Unkelbach and Greifeneder 2013b; Garcia-Marques, Silva, Mello, and Hansen 2019).¹⁵⁴ In the special case of FOF it has been argued that the FOF is most pronounced when the perceptual processing of a stimulus is fast in the sense of being faster than expected for comparable stimuli. That is, the processing is fast relative to a stored standard or expectation for how much time perceptual processing usually takes for stimuli of a similar kind. In relation to strong FOFs Whittlesea and Williams explain:

[S]trong feelings of familiarity are seldom elicited by faces one knows well (e.g., spouse, friends, etc.) or faces one does not know at all (e.g., strangers in a crowd). Instead, strong feelings of familiarity seem to occur when one has limited knowledge, for example, having met the person only a few times (true familiarity) or when a complete stranger resembles someone one knows (false familiarity). We suspected that these outcomes occur because people expect known faces to be fluently processed and nonfluently processed faces to be unknown; that is, they expect a match between the fluency of per-ceiving and the coming-to-mind of identity information. Fluent processing

153The “absolute” in “absolute fluency” needs to be qualified though: an absolutely fluent process is hypothesised to be behind a response time that is (by some margin) below the average response time in a task (Whittlesea and Leboe 2003, p. 63). Insofar, “absolute fluency” is in a way clearly relative, namely relative to the average of the response latencies in a task.

154A special case of 2) is when the speed of one and the same process is discrepant between differing stimulus or item categories, e.g. between low-frequency vs. high-frequency words (Jacoby and Dallas 1981). Assuming that the processes that take in low- and high-frequency words are the same, a high-frequency word encountered amidst low-frequency words will be processed relatively faster.

of a friend’s face meets this expectation; so does nonfluent processing of a stranger’s face. However, limited prior experience, or similarity to a friend, may augment the fluency of processing a current face without enabling re-trieval of identity for that face. In that case, the fluency is surprising. We suspected that in such cases, people unconsciously attribute the unexplained fluency to a prior experience and consciously experience a feeling of familiar-ity. By this account, the basis of the feeling of familiarity is the perception of a discrepancy between the fluency of processing and failure to produce the person’s identity, rather than the fluency per se. (Whittlesea and Williams 2000, p. 548)

I suggest the following reconstruction of this line: an unexpectedly fluently processed stimulus paired with the unavailability of stimulus-related information leads to a FOF and, additionally, a FOU, that frames the FOF as salient and in need of explanation. In other words, perceptual fluency coupled with a poor (disfluent) recall of stimulus-related information (low amount) leads to a strong FOF which is rendered phenomenally salient by a (component) FOU.

Note that FOF research has been so far focusing on familiarity with perceptible material objects. As a consequence, the specific familiarity in question is in most casesperceptual familiarity. As I have noted in section 5.2, however, it seems plausible that also non-perceptible entities can be familiar, such as abstract objects, ideas or mental states, resulting in something like intellectual, conceptual or introspective familiarity.¹⁵⁵ As noted in section 5.2, FOFs are transmodal and can unite with (or be absent from) all kinds of conscious mental states.

My tentative suggestion is that the FOF can be more generally conceptualised as a form

155In fact, the case of introspective familiarity is interesting in that something similar might be at the heart of what has been called the “feeling of pastness” (FOP) that accompanies episodic memory (e.g. James 1890, p. 605; Russell 1921, pp. 161 sq.; Klein 2013; Klein 2014; Dokic 2014a). The FOP phenomenally demarcates a specific content as being from the autobiographical past. James remarked that “we have a constant feelingsui generis of pastness, to which every one of our experiences in turn falls a prey” (James 1890, p. 605) and Russell noted its kinship with the feeling of familiarity:

There may be a specific feeling which could be called the feeling of “pastness,” especially where immediate memory is concerned. [...] [I]mages are regarded by us as more or less accurate copies of past occurrences because they come to us with two sorts of feelings: (1) Those that may be called feelings of familiarity; (2) those that may be collected together as feelings giving a sense of pastness. The first lead us to trust our memories, the second to assign places to them in the time-order. (Russell 1921, pp. 161 sq.)

I suggest that we can develop accounts of the feeling of pastness inspired by the FOK and FOF (which, in contrast, seem to be specific to semantic instead of episodic memory).

of phenomenal familiarity or acquaintance, including perceptual, intellectual, concep-tual and introspective forms. And here (discrepant) processing fluency, taking various process-specific forms, emerges as an ideal determinant of these various kinds of phenom-enal acquaintances: there are fluencies of the perceptual, conceptual, encoding, retrieval etc. kind. It is natural to assume that, in some contexts, conceptual, retrieval or en-coding fluency will lead to a FOF with an idea. On second thought, one of the stimuli classes frequently utilised in FOF research bears actually some resemblance with imma-terial objects: words (e.g. Whittlesea 1993). Plausibly it is not only perceptual fluency that can be triggered by words but also fluency of linguistic processing, resulting in conceptual fluency and familiarity (see also sections 6.3 and 8.2).

5.3.2.2. Exhibit 6: Matching Memory or Accessibility revisited

Notwithstanding the dominant (discrepant) processing fluency account of the FOF, there is a little-noticed but plausible alternative suggestion for explaining the FOF. Interest-ingly, this so-called mnemonic account bears significant resemblance to the accessibility account of the FOK:

[A]n item feels familiar because it matches a representation of a previous encounter. Of course, one would rarely expect such a match to be exact, because the surrounding context, the perceptual conditions, even integral parts of an item can change over time. Thus, it would make functional sense for familiarity to vary continuously with the degree of match. This allows familiarity to be informative, given the fluctuating environment, but it also means that familiarity is fundamentally ambiguous, because even novel items will bear some resemblance to things encountered in the past. [...] [M]emory evidence is a continuous dimension that represents some aggregate of the matches between a recognition probe and the memory images of recently studied items (Verde et al. 2010, p. 144).

Thus, encountering a stimulus prompts a spontaneous attempt to match the stimulus representation with memory content, i.e. to retrieve stimulus-related information (if any). If a sufficient amount of information is retrieved, a FOF is issued.

Note that matching memory for a presently encountered stimulus seems like a close psy-chological approximation of the distal property of actual familiarity. For how else could familiarity be psychologically realised and tracked? In other words, memory matches

are a proxy that is very closely related to the distal property of actual acquaintance.

Thus, if the FOF is caused by memory matches, it would perhaps not be too far fetched to speak of a mechanism approximating direct causation or direct access (assuming a monitor accessing the matches and making an inference).

Be it as it may, as the researchers note themselves, the fluency and the mnemonic account are not mutually exclusive (Verde et al. 2010, p. 150). This makes sense: fluency and memory matches seem to be better evidence for actual familiarity than each of them alone. I thus suggest understanding the FOF analogously to the dynamically unfolding and multiply determined FOK: perceptual fluency gives rise to an early FOF and an ensuing retrieval attempt supplements available information about the stimulus (if any), possibly resulting in the recollection of some stimulus-related information and a FOA that “normalizes” the (expected) FOF. If the perceptual-fluency-prompted second retrieval stage fails, however, a FOU makes the FOF stand out and unexpected.