Consider this following representation of twelve sounds. Each sound differs from its neighbours by the same amount as any other sound. Most people would not be able to discriminate two adjacent sounds ...

... except for in two special cases (one around -3 to -1 and one around +1 to +3) where the discrimination is easier. Here people tend to report hearing the sound change from ba to da or from da to ga.

So although one comparably distant pair of sounds are, from a narrowly acoustic point of view, no more different from each other than any other comparably distant pair of sounds ...

... the sounds in this pair are easy to discriminate.

Coarticulation, the fact that the acoustic effects of phonetic gestures overlap, complicates the relation between sounds and speech. But I want to simplify things by ignoring that here.

Because of the effects of factors such as phonetic context, some things which are acoustically quite unrelated ...

... are nevertheless be identified as the same phonetically.

Conversely, it is possible for the same acoustic simulus to correspond to different phonetic gestures.

This is because the locations of category boundaries change depending on contextual factors such as the speaker’s dialect or the rate at which the speaker talks ; both factors dramatically affect which sounds are produced.

So which features of the stimuli does speech perception track?

Liberman and Mattingly argue that, in the case of speech, the function of speech perception is to track to differences between intended phonetic gestures.

Here are artificial speech-like stimuli for two syllables, [ra] and [la].

The syllables have the same “base” but differ in the “transition”.

When a “transition” is played alone, it sounds like a chirp and quite unlike anything we normally hear in speech. This is part of a general phenomenon: recognizing a stimulus as speech alters how it is processed acoustically, so that some acoustic details are ignored.

Why is this relevant? If there is just one system for processing sounds and speech, then any given stimulus can either be speech or nonspeech but not both. So if there is just one system for processing sounds and speech, it should not ever be possible to process a stimulus in such a way that a single subject reports hearing both the chirp and also the phoneme.

By contrast, if there are two systems then each can make a decision about whether a given stimlus is speech. And although they should generally make the same decision, there could be occasions on which one system decides that a stimulus is nonspeech wheras the other system decides that it is speech. That is, \textbf{multiple systems make possible what a single system rule out: a single stimulus is simultaneously classified as speech and as nonspeech}.

So the conjecture that there are two different systems for identifying sounds and phonetic gestures distinctively predicts that it should be possible, even if only in very special circumstances, for a single stimulus to be simultaneously classified as speech and as nonspeech.

Liberman and colleagues set out to confirm this prediction by studying what they call ‘duplex perception’ \citep{Liberman:1981xk}.\footnote{ In this presentation I have simplified some details of their method and omit controls.}

Duplex perception occurs when the base and transition are played together but in separate ears. In this case, subjects hear both the chirp that they hear when the transition is played in isolated, and the syllable [la] or [ra]. Which syllable they hear depends on which transition is played, so the stimulus must have been classified as speech. But because subjects hear the chirp we also know that the stimulus was not classified as speech in acoustic processes.

This shows that auditory and speech processing involve distinct systems.

\textbf{Representational momentum suggests that there are automatic processes which predict the future trajectories of physical objects.}

Fix shape and density. How would increasing the object’s size affect how quickly it decelerates when launched vertically? Impetus: larger size entails greater deceleration (so slower ascent). Newtonian: larger size entails lower deceleration (so faster ascent) if considering air resistance; otherwise size makes no difference.

This is a doubly exciting result.

It allows us to run the Argument From Jein: \textbf{a conjecture about multiple systems can sometimes be distinguished from a competing conjecture about a single system because multiple systems make possible what a single system rule out: incompatible responses to a single stimulus.}

But even more convincingly, the prediction generated by Kozhevnikov and Heggarty’s conjecture about the computational description of the system underpinning representational momentum has been directly confirmed.

So while not decisive, I take this to be strong evidence for a \textbf{vertical distinction} between two systems for physical cognition.

Let me pause to spell out the pattern as I think Kozhevnikov and Heggarty have provided us with a good model for evaluating claims about vertical distinctions between two systems.

One way to show that mindreading is automatic is to give subjects a task which does not require tracking beliefs and then to compare their performance in two scenarios: a scenario where someone else has a false belief, and a scenario in which someone else has a true belief. If mindreading occurs automatically, performance should not vary between the two scenarios because others’ beliefs are always irrelevant to the subjects’ task and motivations.

\citet{Schneider:2011fk} did just this. They showed their participants a series of videos and instructed them to detect when a figure waved or, in a second experiment, to discriminate between high and low tones as quickly as possible. Performing these tasks did not require tracking anyone’s beliefs, and the participants did not report mindreading when asked afterwards.

on experiment 1: ‘Participants never reported belief tracking when questioned in an open format after the experiment (“What do you think this experiment was about?”). Furthermore, this verbal debriefing about the experiment’s purpose never triggered participants to indicate that they followed the actor’s belief state’ \citep[p.~2]{Schneider:2011fk}

Nevertheless, participants’ eye movements indicated that they were tracking the beliefs of a person who happened to be in the videos.

In a further study, \citet{schneider:2014_task} raised the stakes by giving participants a task that would be harder to perform if they were tracking another’s beliefs. So now tracking another’s beliefs is not only irrelevant to performing the tasks: it may actually hinder performance. Despite this, they found evidence in adults’ looking times that they were tracking another’s false beliefs. This indicates that ‘subjects … track the mental states of others even when they have instructions to complete a task that is incongruent with this operation’ \citep[p.~46]{schneider:2014_task} and so provides evidence for automaticity.% \footnote{% % quote is necessary to qualify in the light of their interpretation; difference between looking at end (task-dependent) and at an earlier phase (task-independent)? %\citet[p.~46]{schneider:2014_task}: ‘we have demonstrated here that subjects implicitly track the mental states of others even when they have instructions to complete a task that is incongruent with this operation. These results provide support for the hypothesis that there exists a ToM mechanism that can operate implicitly to extract belief like states of others (Apperly & Butterfill, 2009) that is immune to top-down task settings.’ It is hard to completely rule out the possibility that belief tracking is merely spontaneous rather than automatic. I take the fact that belief tracking occurs despite plausibly making subjects’ tasks harder to perform to indicate automaticity over spontaneity. If non-automatic belief tracking typically involves awareness of belief tracking, then the fact that subjects did not mention belief tracking when asked after the experiment about its purpose and what they were doing in it further supports the claim that belief tracking was automatic. }

Further evidence that mindreading can occur in adults even when counterproductive has been provided by \citet{kovacs_social_2010}, who showed that another’s irrelevant beliefs about the location of an object can affect how quickly people can detect the object’s presence, and by \citet{Wel:2013uq}, who showed that the same can influence the paths people take to reach an object. Taken together, this is compelling evidence that mindreading in adult humans sometimes involves automatic processes only.

I can't explain it in detail here, but minimal theory of mind is like impetus mechanics. It's obviously flawed and gets things quite wildly wrong but still useful in a limited range of circumstances.

Butterfill and Apperly's minimal theory of mind identifies a model of the mental.

I'm not going to describe the construction of minimal theory of mind, but I've written about it with Ian Apperly and outlined the idea on your handout.

The construction of minimal theory of mind is an attempt to describe how mindreading processes could be cognitively efficient enough to be automatic. It is a demonstration that automatic belief-tracking processes could be mindreading processes.

For this talk, the details don't matter. What matters is just that it's possible to construct minimal models of the mental which are powerful enough that using them would enable you to solve some false belief tasks.

One signature limit on minimal models of the mental concerns false beliefs about identity. These are the kind of false belief Lois Lane has when she falsely believes that Superman and Clark Kent are different people: for the world to be as she believes it to be, there would have to be two objects rather than one; her beliefs expand the world.

(This is for illustrating mistakes about identity.) You might not realise that your bearded drinking pal ‘Ian’ and the author ‘Apperly’ are one and the same person.

[Explain why minimal models can't cope with false beliefs about identity.] Now on a cananical model of the mental, false beliefs involving identity create no special probelm. This is because the (Fregean) proposition that Superman is flying is distinct from the proposition that Clark Kent is flying. Different propositions, different beliefs. By contrast, a minimal model of the mental uses relational attitudes like registration; this means that someone using a minimal model is using the objects themselves, not representational proxies for them, to keep track of different beliefs. Consequently knowing that Superman is Clark Kent prevents a minimal mindreader from tracking Lois’ false beliefs about identity.

This is why false beliefs about identity are a signature limit of minimal models of the mental.

Given that we can coherently make testable hypotheses about models, I want to finish by considering one for which a variety of evidence has recently been offered.

There is some evidence that this prediction is correct. Jason Low and his collegaues set out to test it. They have now published three different papers showing such limits; and Hannes Rakoczy and others have more work in progress on this. Collapsing several experiements using different approaches, the basic pattern of their findings is this ...

Take non-automatic responses first; in this case, communicative responses. When you do a false-belief-identity task, you see the pattern you also find for false-belief-locations tasks. But things look different when you measure non-automatic responses ...

The non-automatic responses all show the signature limit of minimal models of the mental. This is evidence for the hypothesis that Some automatic belief-tracking systems rely on minimal models of the mental.

I also hear that quite a few scientists have pilot data that speaks against this signature limit.

One particular task for future research will be to examine whether other automatic responses to scenarios involving false beliefs about identity, such as response times and movement trajectories, are also subject to this signature limit.

Just say that you can do this with other stimuli and paradigms, and we have done this with infants and would like to do it with adults.

These findings complicate the picture: is helping driven by automatic processes only? If not, why do we predict that the signature limit of minimal theory of mind is found in this case too?

Scott and colleagues \citep{scott:2015_infants} provided other evidence suggesting that infants’ mindreading may be relatively sophisticated. Specifically, 17-month-olds watched a thief attempt to steal a preferred object (a rattling toy) when its owner was momentarily absent by substituting it with a less-preferred object (a non-rattling toy). Infants looked longer when the thief substituted the preferred object with a non-visually-matching silent toy compared to when the thief substituted it with a visually-matching silent toy. The authors postulated that infants can ascribe to the thief an intention to implant in the owner a false-belief about the identity of the substituted toy. The authors further suggested that infants make such ascriptions only when the substitution involves a visually-matching toy and the owner will not test whether the toy rattles on her return.

However, Scott et al.’s \citep{scott:2015_infants} explanations also require postulating that infants take the thief to be strikingly inept; despite having opportunity simply to pilfer from a closed box known to contain at least three rattling toys, the thief engages in elaborate deception which will be uncovered whenever the substituted toy is next shaken and the thief, as sole suspect, easily identified. A further difficulty is that factors unrelated to the thief’s mental states vary between conditions, such as the frequencies with which toys visually matching one present during the final phase of the test trial have rattled. These considerations jointly indicate that further evidence would be needed to support the claim that humans’ early mindreading capacity enables them to ascribe intentions concerning false beliefs involving numerical identity.