Dead Men Do Tell Tales: An Ashlynn Acosta Intuitive Discoveries Mystery

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This presumably reflects some form of an accumulator that is able to track the elapsed time within a session. Accumulation of time is thought to enter into a short-term memory value that is regularly compared with a learned clock criterion value held in long-term memory although see Bizo and White [] for an alternative model of timing via reinforcement accumulation. The clock criterion value of the switch point is thought to be based on an aggregate of recently experienced temporal durations of reversals from recent sessions.

During each session, the timed interval begins at the start of a session and ends once the task reversal occurs. This most recent value is averaged into the values from previous sessions, which form the basis of the criterion clock value. The output of this timing mechanism serves as the endogenous switching cue between the two tasks. The changing amount of activation between these two competing tasks, as mediated by time, is reflected in the sigmoidal switching function of MSR.

From this combination of these cues, the internal competition between the two task representations and its resolution are at the core of MSR and its implications for understanding animal behavior. Figure 4. A model for how the two competing behaviors to Task 1 and Task 2 are represented based on input received from discriminative and contextual stimuli and the temporal clock that modulates behavioral choices over the session.

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Can we better characterize the properties of this internal competition between the representational states that determine choice behavior? For instance, does the increased competition between the two tasks near the transition change how quickly animals respond across a session as measured by reaction time RT? RT could differ over the session if, for example, the increased competition near the reversal resulted in longer choice times. Another possibility is that the simultaneous activation of both tasks near the reversal might result in faster responding on these trials.

Here they might only need to encounter a single stimulus to make a choice as either stimulus might rapidly activate an independent representation, resulting in immediate responses to whichever stimulus was first encountered. Finally, RT may not be affected by the level of competition between the two tasks and therefore remain steady across the session. Figure 5 shows choice RT data from two MSR experiments involving either a simple or a conditional discrimination.

The overall pattern in both studies suggests that RT does not vary systematically in the way that behavioral choice changes across trials. This effect was consistently seen across birds, suggesting that they needed a few trials to get into the more regular pattern of behavior seen for the remainder of the session. This effect may merit further research, as it may indicate a critical period where the processes controlling behavior from previous sessions are reactivated, or it could simply be that some pigeons would benefit from a period of darkness in the chamber prior to the start of the first trial in order to acclimate to the chamber.

Further research would be needed to clarify this issue. In any case, the overall pattern of results support the idea that RT is not affected by the level of competition between the two tasks in the same way that behavioral choice is controlled. Figure 5. Reaction time for simple open squares and conditional closed circles MSR discriminations as a function of percentage into session. The dotted line indicates the reversal location. However, there were differences in RT among individual birds that might merit more investigation.

One conditional bird did seem to slow down in making its test choices just after the reversal.

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This suggests there might be increased competition at this point. That said, this effect was not observed in the other two birds. Furthermore, the slower RTs for the simple discrimination in comparison to the conditional discrimination task also reflect one bird that was much slower than the others although the overall function was still flat.

Although more research is needed to clarify such details, the processes resolving the competition in the middle of the session seem to not dramatically affect or interfere with choice time.

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As a general rule, and aside from the warm-up effect, the birds appear to take approximately the same time to respond on a trial independent of the level of competition present between tasks. The shape of such averaged functions can stem from two different sources. First, the shape might represent the averaging of a collection of sessions in which the animal makes a single switch from performing Task 1 to Task 2. Averaging these variable, single switch points across a number of sessions may produce the gradual transition seen during the midpoint of the session.

A second possibility is that the middle part of the function represents a period of ongoing competition between the two tasks. Thus, there is an intermediate transition period where the relative activations of the two task representations overlap enough to cause a large number of alternating responses across the choice stimuli.

This results in multiple switches across the tasks in each session. In this possibility, the sigmoidal shape of the average function is a direct representation of the degree of this competition within a single session. The best way to examine these alternatives is to look at the behavior of individual birds from single sessions. Is a typical session characterized by a single switch from one task to the other task, or is it comprised of a region of multiple switches?

Since each session might only contain a single switch or data point at the transition of each session, a large number of sessions from different animals is needed. In these sessions, time was the only switching cue available, although these time-only sessions were embedded within ongoing sessions that had other external switching cues available. We examined only the time-only sessions for each bird to explore the question at hand.

We found evidence indicative of both single-switch and multiple-switch representations. We selected these two birds because they each best represent the range of patterns observed. The left panel shows four representative sessions from one bird, 2L, that most frequently and regularly exhibited a single switch from responding Task 1 to Task 2 within a session.

In the top leftmost panel, this bird made 42 consecutive choice responses to Task 1, followed by 38 successive choice responses to Task 2. This single switch sometimes came before or after, but always near, the reversal. The other three sessions depicted show a similar behavioral pattern.

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This pattern was typical for bird 2L. This is depicted in the schematic at the bottom of Figure 6, which shows an initial region of choice behavior dominated by choice of Task 1, a smaller intermediate region where there is increasing overlap and competition in the control of responding between the two tasks, and a large terminal region where responses are strongly controlled by the choice of the second task. Figure 6. Gray symbols indicate correct choices, with circles indicating choice of Task 1 and triangles indicating choice of Task 2.

Red circles indicate perseverative errors on Task 1, while green triangles indicate anticipatory errors to Task 2. The second pigeon, 1B, exhibited a different profile. In contrast to pigeon 2L, this bird showed a much larger intermediate period where there was considerable competition between the two task representations for control of behavior. In the top rightmost panel, this pigeon responded initially to the correct choice from Task 1, but then suffered a number of separate intrusions from Task 2 as it neared the reversal.

After the reversal, there was also an extended period of perseveration from Task 1 before a final and terminal switch to Task 2. As can be seen in the figure, the other example sessions for this pigeon show similar patterns of multiple switches from Task 1 to Task 2 around the reversal. The various switches between responding to the two tasks are clearly temporally related, as they cluster towards the middle of the session.

The schematic at the bottom of Figure 6 captures this increased intermediate phase where the two tasks competed for behavior and smaller sections of strongly controlled behaviors at the session endpoints. The two other birds not shown from this experiment landed somewhere in between the patterns of the first and second bird. One bird from the experiment looked more similar to pigeon 2L, but with a few more tightly grouped switches per session.

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From these results, it appears that MSR has three broad phases. Between those phases is an intermediate phase where ongoing competition between the two tasks is much higher. The duration of this middle region seems to vary among birds depending on their approach to the task and their ability to segregate the two portions of the session. We tried to capture the size of this intermediate phase of competition by looking at the trial locations where the first and last errors occurred within a session.

This is not a perfect measure.

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Pigeons make errors that likely do not have much to do with competition e. Thus, the first and last errors do not precisely mark the onset and offset of competition. Nonetheless, this easily computed measure does provide boundaries on the period over which the representations of each task and the mechanisms controlling responding to Task 1 and 2 appear simultaneously active. The other bird 1B , however, showed a wider range of These values were The above pattern indicates that animals in MSR typically engage in medium to long runs of Task 1 responses before beginning to suffer from anticipation interference from Task 2, followed by medium to long runs of Task 2 responses after an intermediate period of perseveration on Task 1.

To capture the character of these two extended runs, we next analyzed the starting location within a session of where the longest run of correct responding to Task 1 and Task 2 occurred. We determined for each of the 40 sessions the trial where the longest sequence of correct responding started for both tasks. The resulting pattern is shown in Figure 7. This figure shows the relative frequency distribution of the starting trial position for the longest runs of Task 1 and for those of Task 2. The results show that the pigeons consistently begin responding correctly to Task 1 on Trial 1 or 2 and repeat this response for an extended period of the first half of the session.

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As can be seen in the figure, only infrequently did these runs start later than Trial 5 over this portion of the session be observant of the break point on the y -axis. The results for Task 2 are more variable as might be expected given their later location in a session. The distribution of the longest Task 2 runs begins prior to and peaks just after the reversal location, reflecting the regular initiation of the longest Task 2 runs around the reversal.

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The greater variability in Task 2 run behavior may reflect greater cue competition than is present at the start of the session.