Decision-making with multiple alternatives

The mean difference in firing rate between the 4-choice and 2-choice tasks before motion onset was 16.1±1.6 sp/s lower on the 4-choice task (p<10−5).

“It was subtly apparent in the transient target onset response and then was prominent until motion onset (mean difference = 16.1±1.6 sp/s, p<10−5, Fig. 3c, arrow).”

The effect of reduced firing rate on the 4-choice task before motion onset was statistically significant in both monkeys (Monkey I: 15.5±1.8 sp/s, p<10−5; Monkey S: 18.8±2.6 sp/s, p<10−4).

“This effect was statistically significant in both monkeys (Monkey I: mean difference, 15.5±1.8 sp/s, p<10−5 Monkey S: 18.8±2.6sp/s, p<10−4).”

On a 2- and 4-choice direction discrimination decision task, firing rates in the lateral intraparietal area appeared to reflect the accumulation of evidence for or against each choice.

“For both tasks, firing rates in the lateral intraparietal area appeared to reflect the accumulation of evidence for or against each choice.”

Shortly after motion onset, LIP responses showed a brief dip followed by a gradual rise in firing rate.

“Shortly after onset, the responses showed a brief dip (Fig. 2a,c, middle panel), followed by a gradual rise in firing rate.”

The relationship between buildup rate and motion strength was similar on the 2- and 4-choice tasks.

“This relationship was similar on 2- and 4-choice tasks.”

The reduced firing rate on the 4-choice task persisted after motion onset.

“The reduced firing rate on the 4-choice task persisted after motion onset.”

Near the saccade, the neural correlate of motion strength vanished.

“Near the saccade, however, this neural correlate of motion strength 1,2,15 vanished (Fig. 2a,c, right).”

• cites [1] Gold, J.I. & Shadlen, M.N. The neural basis of decision making. Annu. Rev. Neurosci. 30, 535–574 (2007). sourceNot checked yet

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• cites [2] Roitman, J.D. & Shadlen, M.N. Response of neurons in the lateral intraparietal area during a combined visual discrimination reaction time task. J. Neurosci. 22, 9475–9489 (2002). sourceNot checked yet

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• cites [15] Cook, E.P. & Maunsell, J.H. Dynamics of neuronal responses in macaque MT and VIP during motion detection. Nat. Neurosci. 5, 985–994 (2002). sourceNot checked yet

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Evidence accumulation began at a lower firing rate for the 4-choice task than for the 2-choice task.

“Evidence accumulation began at a lower firing rate for the 4-choice task, but reached a common level at the end of the decision process.”

Early in the decision process, decision outcome has only a weak effect on neural responses.

“Early on, decision outcome has only a weak effect on the neural responses.”

The effect of choice on firing rate is most conspicuous late in the decision process.

“The effect of choice is most conspicuous late in the decision process (Fig. 5a–d).”

Decision speed depended on motion strength and the number of choices.

“Like accuracy, decision speed also depended on motion strength and the number of choices.”

Evidence accumulation reached a common level at the end of the decision process for the 2- and 4-choice tasks.

“Evidence accumulation began at a lower firing rate for the 4-choice task, but reached a common level at the end of the decision process.”

The reduced firing rate on the 4-choice task was evident across the population of neurons tested.

“The reduced firing rate on the 4-choice task was evident across the population of neurons tested (Fig. 3b,c).”

Between target appearance and motion onset, there was a clear difference in firing rates between the 2- and 4-target conditions.

“Between target appearance and motion onset, there was a clear difference in firing rates between 2- and 4-target conditions (Fig. 3).”

After the dip, the rate of increase in firing rate depended on motion strength.

“After the dip, the rate of increase in firing rate depended on motion strength (Fig. 2a,c middle).”

In the example neuron, responses were 11.9±4.0 sp/s lower on the 4-choice task (p<0.003).

“In the example (Fig. 3a), responses were 11.9±4.0 sp/s lower on 4-choice task (p<0.003).”

The stereotyped firing rate at the end of the decision is clearer when responses are grouped by reaction time instead of motion strength.

“The stereotyped firing rate at the end of the decision is clearer when responses are grouped by RT (4 choice: Fig. 2b,d; 2 choice: Supplementary Fig. 2a) instead of motion strength.”

Following the dip, there was a time-dependent rise in firing rate (buildup).

“Following the dip, there was a time-dependent rise in the firing rate (“buildup”).”

Buildup rates scale approximately linearly as a function of motion strength for motion toward and away from the neuron's response field.

“Buildup rates scale approximately linearly as a function of motion strength for motion toward and away from the neuron’s RF.”

The 70 neurons recorded had spatially selective persistent activity on delayed and memory-guided eye movement tasks.

“The 70 neurons recorded in our experiment had spatially selective persistent activity on delayed and memory-guided eye movement tasks (Supplementary Fig. 1).”

During the dip after motion onset, firing rates were 9.17±1.05 sp/s lower for the 4-choice than for the 2-choice task (p<10−5).

“During this dip, firing rates were 9.17±1.05 sp/s lower for the 4-choice than for the 2-choice task (Supplementary Fig. 3, p<10−5).”

Reaction times were longer on the 4-choice task than on the 2-choice task.

“RTs were longer on the 4-choice task10.”

• cites [10] Hick, W.E. On the rate of gain of information. Q. J. Exp. Psychol. 4, 11–26 (1952). sourceNot checked yet

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The difference in firing rates just preceding Tin choices amounts to only 3.7% of the firing rate in this epoch.

“Although significant, this difference amounts to only 3.7% of the firing rate in this epoch.”

During the dip at the beginning of motion, 2-choice responses were 2.66±2.0 sp/s higher than 90° responses (p=0.10).

“This reduction became more modest through the “dip” during the beginning of motion (2-choice responses were 2.66±2.0 sp/s higher than 90° responses, p=0.10), followed by a buildup in firing rates leading to the decision.”

There is evidence for a threshold on the 4-choice task as well.

“We see evidence for a threshold on the 4-choice task as well (Fig. 2d).”

Longer viewing durations were required for the same accuracy.

“Longer viewing durations were required for the same accuracy (Fig. 1f, g).”

A major difference between the 2- and 4-choice responses was the firing rate at the beginning of the decision process.

“A major difference between 2- and 4-choice responses was the firing rate at the beginning of the decision process (Fig. 3), consistent with the inverse relationship between the number of possible eye movement directions and firing rates in the superior colliculus preceding a saccade instruction 30.”

• cites [30] Basso, M.A. & Wurtz, R.H. Modulation of neuronal activity in superior colliculus by changes in target probability. J. Neurosci. 18, 7519–7534 (1998). sourceNot checked yet

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The rise in firing rate that depends on time but not on motion strength or direction (u(t), urgency) is larger in the 2-choice task.

“The rise in firing rate that depends on time but not on motion strength or direction (u(t), urgency) is larger in the 2-choice task (Supplementary Fig. 6b, c).”

The model accounts for the longer reaction times observed on error trials for both the 2- and 4-choice task.

“The model also accounts for the longer RTs observed on error trials for both the 2- and 4-choice task (Supplementary Fig. 7).”

• AssumptionThe authors state this as an assumption: The decision process can be modeled as a race between 2- or 4-choice mechanisms that determines which target will be selected.
• AssumptionThe authors state this as an assumption: Each choice mechanism accumulates momentary evidence in favor of the choice target in its response field.
• AssumptionThe authors state this as an assumption: A decision ensues when one of the accumulators reaches a bound.

The change in excursion in the 4-choice task was confirmed in the subset of neurons tested on the 90° control task (mean difference 4.2±2.3 sp/s larger for 4-choice than for 2-choice, p<0.04).

“The change in excursion in the 4-choice task was also confirmed in this subset of neurons (mean difference 4.2±2.3 sp/s larger for 4-choice than for 2-choice, p<0.04).”

The excursion of LIP firing rates throughout the decision is larger on the 4-choice task.

“The excursion of LIP firing rates throughout the decision is larger on the 4-choice task (Fig. 6).”

Stronger motion in orthogonal directions reduced the firing rate slightly (slope = −0.33±0.09 sp.s−2.%coh−1, p<10−3).

“Stronger motion reduced the firing rate slightly (Fig. 4f, slope of red dot-dash trace = −0.33±0.09 sp.s−2.%coh−1, p<10−3).”

Firing rates just preceding Tin choices were similar for the 2- and 4-choice trials (on average only 3.1±1.3 sp/s higher for 4-choice, p<0.03).

“Firing rates just preceding Tin choices were similar for 2- and 4-choice trials (Fig. 5a,c; responses in shaded region were on average only 3.1±1.3 sp/s higher for 4-choice than for 2-choice, p<0.03).”

For motion toward T90 on the 90°-control task, a 1% increase in motion strength decreased buildup rate.

“However, for motion toward T90, a 1% increase in motion strength decreased buildup rate.”

The magnitude of the urgency signal u(t) on the 90°-control task fell between those measured on the 2- and 4-choice tasks.

“The magnitude of this urgency signal, u(t), fell between those measured on the 2- and 4-choice tasks (Table 1; Supplementary Fig. 6c).”

The inverse correlation between buildup rate and reaction time was typical of the data (2-choice: mean correlation coefficient −0.22±0.02, p<10−5, N=70 neurons; 4-choice: mean correlation coefficient −0.26±0.02, p<10−5, N=69).

“This observation was typical of the data (Fig. 7c,d; 2-choice: mean correlation coefficient was −0.22±0.02, p<10−5, N=70 neurons; 4-choice: mean correlation coefficient was −0.26±0.02, p<10−5, N=69).”

For motion toward Tin, buildup-rate slopes differed by only 0.17±0.45 sp.s−2.%coh−1 between the 2- and 4-choice tasks (p=0.71).

“For motion toward Tin, these slopes differed by only 0.17±0.45 sp.s−2.%coh−1 (Fig. 4f, p=0.71, parallel solid lines).”

The initial response when motion began was lower for the 4-choice task than for the 2-choice task.

“However, the initial response when the motion began was lower for the 4-choice task than the 2-choice task (Fig. 3).”

Trial-to-trial variability in buildup rate was inversely correlated with trial-to-trial variability in reaction time.

“Trial-to-trial variability in buildup rate was inversely correlated with trial-to-trial variability in RT, despite the noisy estimate of buildup rate and large variation in RT.”

The effect of motion strength on buildup rates on the 90°-control task was similar to 2-choice responses for motion toward Tin (slopes differed by 0.23±0.32 sp.s−2.%coh−1, p=0.47).

“The effect of motion strength on these buildup rates was similar to 2-choice responses for motion toward Tin (Figure 4g; for the population, slopes differed by 0.23±0.32 sp.s−2.% coh−1, p=0.47).”

When choices were to the target in the neuron's response field, firing rates for the 2- and 4-choice tasks ultimately reached a similar value near the time of the saccade.

“When choices were to the target in the neuron’s RF, firing rates for the 2- and 4-choice task ultimately reached a similar value near the time of the saccade (Fig. 2d, Supplementary Fig. 2a).”

The 90° separation in a 2-choice task increased difficulty slightly.

“Although this angle remains large compared to fine discriminations that humans and monkeys can make 22–24, it did increase difficulty slightly, as shown by 90° separation in a 2-choice task.”

• cites [22] Jazayeri, M. & Movshon, J.A. A new perceptual illusion reveals mechanisms of sensory decoding. Nature 446, 912–915 (2007). sourceNot checked yet

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• cites [23] Purushothaman, G. & Bradley, D.C. Neural population code for fine perceptual decisions in area MT. Nat. Neurosci. 8, 99–106 (2005). sourceNot checked yet

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• cites [24] Churchland, A.K. et al. Directional anisotropies reveal a functional segregation of visual motion processing for perception and action. Neuron 37, 1001–1011 (2003). sourceNot checked yet

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Firing rates build up faster in association with strong motion and fast reaction time.

“We have already noted that firing rates build up faster in association with strong motion and fast RT.”

A putative neural correlate of the termination bound is evident in area LIP: for all reaction times and motion strengths, LIP neurons reach a stereotyped firing rate shortly before the monkey initiates a saccade to indicate its choice for Tin.

“A putative neural correlate of this operation is evident in area LIP: for all RTs (and motion strengths), the firing rates of LIP neurons reach a stereotyped level shortly before the monkey initiates a saccade to indicate its choice for Tin (Fig. 2b, d and Supplementary Fig 2a, b).”

The firing rate excursion on the 90° control task was nearly identical to that seen on the standard 2-choice task (mean difference 0.13±0.37 sp/s, p=0.53).

“The firing rate excursion on the 90° control task was nearly identical to that seen on the standard 2-choice task (Fig. 6d; mean difference 0.13±0.37 sp/s, p=0.53).”

The rate of the time-dependent buildup is considerably larger for the 2-choice than for the 4-choice task (2-choice intercept 50.7±8.2 sp/s/s greater than 4-choice intercept, p<10−5).

“It is considerably larger for 2- than for 4-choice (Figure 4f 2-choice intercept 50.7±8.2 sp/s/s greater than 4-choice intercept, p<10−5, also see Discussion & Supplementary Fig. 6b,c).”

The change in LIP buildup rates produced by a change in motion strength toward Tin is similar for the 2- and 4-choice tasks.

“The change in LIP buildup rates produced by a change in motion strength toward Tin is similar for 2- and 4-choice tasks (Fig. 4).”

Before motion onset, activity on the 90°-control trials was slightly reduced in comparison with the standard 2-choice task.

“Recall that before motion onset, activity on the 90°-control trials was slightly reduced in comparison with the standard 2-choice task.”

The total difference in firing rate excursion was 6.11±0.21 sp/s larger for the 4-choice than for the 2-choice task.

“The difference in firing rates at the beginning and end of motion-viewing combined to make a total difference in firing rate excursion of 6.11±0.21 sp/s larger for 4-choice than for 2-choice (see Methods, Eq. 2).”

At the beginning of motion viewing (170-210 ms after motion onset), mean firing rate was 9.2±1.1 sp/s larger for 2-choice than 4-choice trials (p<10−5).

“The arrow indicates the mean difference (9.2±1.1 sp/s larger for 2-choice trials, p<10−5).”

The variance associated with RT groups reached a nadir in the interval 40 to 80 ms before the saccade.

“The variance associated with RT groups reached a nadir in the interval 40 to 80 ms before the saccade.”

• Also stated in: § Supplementary Materials · plain

  “The variance associated with RT groups reached a nadir in the interval 40 to 80 ms before the saccade.”

Responses to the T90 target on the screening saccade task were not lower than responses to the Tout target, as would be expected if they were in an inhibitory surround.

“Second, responses to the T90 target on our screening saccade task were not lower than responses to the Tout target, as would be expected if they were in an inhibitory surround (Supplementary Fig. 1c).”

The urgency u(t) was stronger in the 2-choice than in the 4-choice conditions.

“Third, the urgency, u(t), was stronger in 2- than 4-choice conditions.”

Some oculomotor measures were affected by the number of choices.

“Some of these measures were affected by the number of choices 48,49 (Supplementary Fig. 8).”

• cites [48] Arai, K., McPeek, R.M. & Keller, E.L. Properties of saccadic responses in monkey when multiple competing visual stimuli are present. J. Neurophysiol. 91, 890–900 (2004). sourceNot checked yet

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• cites [49] Walker, R., Deubel, H., Schneider, W.X. & Findlay, J.M. Effect of remote distractors on saccade programming: evidence for an extended fixation zone. J. Neurophysiol. 78, 1108–1119 (1997). sourceNot checked yet

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Motion strength affects the buildup rates even for trials that terminate with the same saccadic choice.

“Motion strength affects the buildup rates even for trials that terminate with the same saccadic choice.”

• Also stated in: § Supplementary Materials · plain

  “Motion strength affects the buildup rates even for trials that terminate with the same saccadic choice.”

A time-dependent buildup of firing rate was observed that is not explained by evidence accumulation.

“We observed a time-dependent buildup of firing rate that is not explained by evidence accumulation.”

The rate of buildup in LIP that can be attributed to motion strength was similar on the 2- and 4-choice configurations for motion toward Tin and for Tin choices.

“Second, the rate of buildup in LIP that can be attributed to motion strength was similar on 2- and 4-choice configurations for motion toward Tin (Fig. 4) and for Tin choices (Supplementary Fig. 4).”

A neural correlate of evidence accumulation was observed in structures that represent the choice.

“Specifically, we observed a neural correlate of evidence accumulation in structures that represent the choice.”

The model with urgency explains the longer RTs on error trials.

“The model with urgency explains the longer RTs on error trials 36 (Supplementary Fig. 7).”

• cites [36] Ditterich, J. Stochastic models of decisions about motion direction: behavior and physiology. Neural Netw. 19, 981–1012 (2006). sourceNot checked yet

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For both 2- and 4-choice tasks, firing rate variance remained at a stable, low value until 190 ms after the onset of stimulus motion, after which it increased dramatically.

“For both 2- and 4-choice tasks, firing rate variance remained at a stable, low value until 190 ms after the onset of stimulus motion, after which it increased dramatically, reflecting the divergence of responses to different stimuli.”

In two experiments, a reduction in firing rate on the 4-choice task was observed even when receptive fields were large enough to encompass the orthogonal targets in their excitatory regions.

“Third, in two experiments, we observed a reduction in firing rate on the 4-choice task even when RFs were large enough to encompass the orthogonal targets in their excitatory regions (data not shown).”

The model performed only slightly worse when T0 was constrained to be the same value for 2- and 4-choice conditions.

“the model performed only slightly worse when T0 was constrained to be the same value for 2- and 4-choice conditions”

The firing rate at the decision's end is similar in the 2- and 4-choice configurations.

“First, the firing rate at the decision’s end is similar in the 2- and 4-choice configurations.”

Stronger motion was associated with larger buildup rates for motion in the Tin direction.

“Stronger motion was associated with larger buildup rates (note the positive slopes).”

The monkeys were unbiased in their choices on 0% coherence trials in all three tasks.

“the monkeys were unbiased in their choices on these trials in all three tasks.”

Based on the 4 traces shown, the rates seem to reach a common endpoint between 40-80 ms before the saccade.

“Based on the 4 traces shown, the rates seem to reach a common endpoint between 40–80 ms before the saccade.”

The mean error magnitude was only 1.41±0.1°.

“the mean error magnitude was only 1.41±0.1°.”

The magnitude of the coherence-dependent change of buildup for Tout motion was greater in the 2-choice task (mean difference = 0.075±0.021 sp·s−2·%coh−1 less negative for 4-choice trials, p<0.001).

“The magnitude of the coherence-dependent change of buildup was greater in the 2-choice task (mean difference = 0.075±0.021 sp·s−2·%coh−1 less negative for 4-choice trials, p<0.001).”

Across the sample of 40 neurons, the overall difference in saccade amplitudes between 2- and 4-choice tasks was negligible (mean percent difference = −0.59±0.46%; p=0.212).

“the overall difference was negligible across our sample (mean percent difference = −0.59±0.46%; p=0.212).”

We observed a time-dependent buildup of firing rate that is not explained by evidence accumulation.

“We observed a time-dependent buildup of firing rate that is not explained by evidence accumulation.”

Saccadic error magnitude showed a trend for less accurate saccades on the 4-choice task (mean percent difference = −4.87±2.03% p<0.03).

“The trend was for less accurate saccades on the 4-choice task (mean percent difference = −4.87±2.03% p<0.03).”

The mean difference in firing rates at the beginning of the motion viewing period (170-210 ms after motion onset) was 9.2±1.1 sp/s larger for 2-choice trials (p<10−5).

“The arrow indicates the mean difference (9.2±1.1 sp/s larger for 2-choice trials, p<10−5).”

The magnitude of the coherence-dependent change in buildup rate for Tin motion was similar for 2- and 4-choice conditions (mean difference = 0.02±0.03 sp·s−2·% coh−1, p=0.53).

“The magnitude of the coherence-dependent change was similar for 2- and 4-choice conditions (mean difference = 0.02±0.03 sp·s−2·% coh−1, p=0.53, arrow).”

Firing rate excursions were significantly larger for 4-choice than for 2-choice responses over a wide range of termination intervals.

“Firing rate excursions were significantly larger for 4-choice than for 2-choice responses over a wide range of termination intervals.”

The mean response to T90 targets is similar to the mean response to Tout targets on the overlap saccade task.

“The mean response to T90 targets is similar to the mean response to Tout targets”

This buildup is seen on 0% coherence motion trials, when the momentary evidence is unbiased for Tin or Tout.

“This is the buildup seen on 0% coherence motion trials, when the momentary evidence is unbiased for Tin or Tout”

Stronger motion was associated with lower buildup rates for motion in the Tout direction.

“Stronger motion was associated with lower buildup rates (note the negative slopes).”

The dip in firing rate seems to mark the beginning of evidence accumulation.

“The dip, observed in other studies 2,12–14, seems to mark the beginning of evidence accumulation.”

• cites [2] Roitman, J.D. & Shadlen, M.N. Response of neurons in the lateral intraparietal area during a combined visual discrimination reaction time task. J. Neurosci. 22, 9475–9489 (2002). sourceNot checked yet

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• cites [12] Leon, M.I. & Shadlen, M.N. Representation of time by neurons in the posterior parietal cortex of the macaque. Neuron 38, 317–327 (2003). sourceNot checked yet

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• cites [13] Sato, T. & Schall, J.D. Pre-excitatory pause in frontal eye field responses. Exp. Brain Res. 139, 53–58 (2001). sourceNot checked yet

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• cites [14] Kiani, R., Hanks, T.D. & Shadlen, M.N. Bounded integration in parietal cortex underlies decisions even when viewing duration is dictated by the environment. J. Neurosci. 28, 3017–3029 (2008). sourceNot checked yet

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The time-dependent rise in firing rates may impose a deadline for deciding.

“Further, on both tasks, we observed a time-dependent rise in firing rates that may impose a deadline for deciding.”

The dip epoch retains much of the difference in firing rate seen before motion onset.

“Thus this epoch retains much of the difference in firing rate seen before motion onset.”

The bounded accumulation framework can be extended to explain more complex decisions with multiple alternatives.

“Our results argue that the bounded accumulation framework can be extended to explain more complex decisions, and they begin to reveal how decision-making circuitry adjusts to increasingly difficult decisions.”

The pattern of LIP activity in the 4-choice task is similar to the process underlying 2-choice decisions.

“This pattern of LIP activity in the 4-choice task is similar to the process underlying 2-choice decisions1,2,16.”

• cites [1] Gold, J.I. & Shadlen, M.N. The neural basis of decision making. Annu. Rev. Neurosci. 30, 535–574 (2007). sourceNot checked yet

  Not checked in the free run.

• cites [2] Roitman, J.D. & Shadlen, M.N. Response of neurons in the lateral intraparietal area during a combined visual discrimination reaction time task. J. Neurosci. 22, 9475–9489 (2002). sourceNot checked yet

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• cites [16] Ratcliff, R. et al. Dual diffusion model for single-cell recording data from the superior colliculus in a brightness-discrimination task. J. Neurophysiol. 97, 1756–1774 (2007). sourceNot checked yet

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Analysis of variability across different reaction-time groups provides quantitative support for a common firing rate close to the end of the trial.

“Analysis of variability across different RT groups provides quantitative support for a common firing rate close to the end of the trial (Supplementary Fig. 2b).”

The more frequent errors at low motion strengths on the 4-choice task may be attributed to a failure to discriminate the direction of motion rather than confusion about action selection.

“Therefore, the more frequent errors at low motion strengths on the 4-choice task may be attributed to a failure to discriminate the direction of motion rather than confusion about action selection.”

The physiological differences between the 2- and 4-choice tasks appear to explain subjects' accuracy and reaction times.

“The differences appear to explain subjects’ accuracy and reaction times.”

The larger firing rate excursion on the 4-choice task suggests that subjects required more evidence before making a choice.

“The larger excursion suggests that subjects required more evidence before making a choice.”

The stereotyped firing rate at decision end may reflect a bound that is common to easy and difficult motion strengths.

“The stereotyped firing rate may reflect a bound that is common to easy and difficult motion strengths.”

In the reaction time version of the motion task, firing rates are similar at decision end when the monkey selects a target in the neuron's response field, for all motion strengths and reaction times.

“Finally, in the RT version, firing rates are similar at decision end when the monkey selects a target in the neuron’s RF, for all motion strengths and RTs.”

• cites [2] Roitman, J.D. & Shadlen, M.N. Response of neurons in the lateral intraparietal area during a combined visual discrimination reaction time task. J. Neurosci. 22, 9475–9489 (2002). sourceNot checked yet

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• cites [7] Shadlen, M.N. & Newsome, W.T. Neural basis of a perceptual decision in the parietal cortex (area LIP) of the rhesus monkey. J. Neurophysiol. 86, 1916–1936 (2001). sourceNot checked yet

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• cites [8] Hanks, T.D., Ditterich, J. & Shadlen, M.N. Microstimulation of macaque area LIP affects decision-making in a motion discrimination task. Nat. Neurosci. 9, 682–689 (2006). sourceNot checked yet

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• cites [9] Huk, A.C. & Shadlen, M.N. Neural activity in macaque parietal cortex reflects temporal integration of visual motion signals during perceptual decision making. J. Neurosci. 25, 10420–10436 (2005). sourceNot checked yet

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These physiological observations constitute an effective strategy for handling increased task difficulty.

“These physiological observations constitute an effective strategy for handling increased task difficulty.”

The monkeys understood the relationship between stimulus direction and choice targets, as revealed by performance with strong motion.

“The performance with strong motion reveals that the monkeys understood the relationship between stimulus direction and choice targets.”

The pattern of LIP activity in the 4-choice task is broadly consistent with a bounded accumulation of evidence among competing response mechanisms.

“The pattern is broadly consistent with a bounded accumulation of evidence among competing response mechanisms.”

The net effect of orthogonal motion is weak negative evidence, on average.

“Although in any one experiment, either T90 direction might provide weak positive evidence for a Tin choice (e.g., Fig. 4e), the net effect of orthogonal motion is weak negative evidence, on average.”

The difference in firing rate excursion is attributed to the number of choices.

“The difference in excursion is attributed to the number of choices.”

Some of the buildup in firing rate on the 90°-control task is not attributed to an accumulation of motion evidence, because it is present even on trials with 0% motion strength.

“As before, some of the buildup in firing rate on the 90°-control task is not attributed to an accumulation of motion evidence, because it is present even on trials with 0% motion strength.”

Motion toward T90 constitutes weak evidence against the Tin choice.

“This suggests that motion toward T90 constitutes weak evidence against the Tin choice.”

The larger excursion and less pronounced time-varying increase would lead to better accuracy on the 4-choice task, were it not for the larger number of choices.

“For example, the larger excursion and less pronounced time-varying increase would lead to better accuracy on the 4-choice task, were it not for the larger number of choices.”

The time-dependent rise is not explained by random fluctuations in motion energy because the increase was evident when trials ending in Tin and Tout choices were averaged together.

“This time-dependent rise is not explained by random fluctuations in motion energy because the increase was evident when trials ending in Tin and Tout choices were averaged together (as in Fig. 4a–d).”

Because firing rates were already lower at the beginning of these trials, the persistence of this difference is only remarkable in contrast with the Tin choices.

“Because firing rates were already lower at the beginning of these trials, the persistence of this difference is only remarkable in contrast with the Tin choices.”

LIP is only weakly affected by motion in directions orthogonal to the Tin-Tout axis on the 4-choice task.

“This analysis also suggests that LIP is only weakly affected by motion in directions orthogonal to the Tin–Tout axis on the 4-choice task.”

The preceding analyses expose the similarities and differences in how LIP activity reflects a bounded accumulation of evidence during 2- and 4-choice decisions.

“The preceding analyses expose the similarities and differences in how LIP activity reflects a bounded accumulation of evidence during 2 and 4 choice decisions.”

The time-dependent rise reflects the cost associated with the passage of time, corresponding to the psychological sense of urgency, u(t).

“We interpret this rise as a reflection of the cost associated with the passage of time, corresponding to the psychological sense of urgency, u(t) 17,18.”

• cites [17] Reddi, B.A. & Carpenter, R.H. The influence of urgency on decision time. Nat. Neurosci. 3, 827–830 (2000). sourceNot checked yet

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• cites [18] Reddi, B.A., Asrress, K.N. & Carpenter, R.H. Accuracy, information, and response time in a saccadic decision task. J. Neurophysiol. 90, 3538–35346 (2003). sourceNot checked yet

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The termination of decisions is associated with a fixed firing rate when the monkey chooses the target in the response field.

“We conclude that the termination of decisions is associated with a fixed firing rate when the monkey chooses the target in the RF.”

The angular separation between choice targets alone is insufficient to cause an increase in firing rate excursion of the magnitude seen on the 4-choice task.

“Thus, the angular separation between choice targets alone is, by itself, insufficient to cause an increase in firing rate excursion of the magnitude seen on the 4-choice task.”

On a variety of 2-choice decision tasks, a threshold crossing is associated with termination of the decision.

“On a variety of 2-choice decision tasks, a threshold crossing is associated with termination of the decision 1,2,19.”

• cites [1] Gold, J.I. & Shadlen, M.N. The neural basis of decision making. Annu. Rev. Neurosci. 30, 535–574 (2007). sourceNot checked yet

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• cites [2] Roitman, J.D. & Shadlen, M.N. Response of neurons in the lateral intraparietal area during a combined visual discrimination reaction time task. J. Neurosci. 22, 9475–9489 (2002). sourceNot checked yet

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• cites [19] Hanes, D.P. & Schall, J.D. Neural control of voluntary movement initiation. Science 274, 427–430 (1996). sourceNot checked yet

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Firing rates at the beginning and end of the motion-viewing period suggest that LIP neurons undergo a larger change in firing rate during decisions among 4 possible alternatives.

“Firing rates at the beginning and end of the motion-viewing period suggest that LIP neurons undergo a larger change in firing rate during decisions among 4 possible alternatives.”

The same bounded accumulation framework applies to decisions among 4 choices.

“Our findings suggest that this same bounded accumulation framework applies to decisions among 4 choices.”

The fit supports the hypothesis that the framework of bounded accumulation can be extended to explain decisions with more than 2 alternatives.

“This fit supports the hypothesis that the framework of bounded accumulation can be extended to explain decisions with more than 2 alternatives.”

The physiological differences on the 2- and 4-choice tasks are of the right size to explain the behavioral differences observed.

“Moreover, the physiological differences on the 2- and 4-choice tasks are of the right size to explain the behavioral differences we observed.”

Differences in behavior between the 2- and 4-choice tasks are not explained by differences in the mapping of motion information onto a change in LIP firing rate.

“Thus, differences in behavior are not explained by differences in the mapping of motion information onto a change in LIP firing rate.”

LIP registers evidence along the Tin-Tout axis similarly for the 2- and 4-choice tasks.

“We conclude that LIP registers evidence along the Tin–Tout axis similarly for 2- and 4-choice tasks.”

The monkeys could afford to terminate choices using a more lax criterion-a shorter excursion to a termination bound-without increasing the average probability of error.

“The monkeys could afford to terminate choices using a more lax criterion — what we interpret as a shorter excursion to a termination bound—without increasing the average probability of error.”

The urgency signal is the time-dependent rise in firing rate that is seen on all trials regardless of motion strength and direction.

“We identified this urgency signal as the time-dependent rise in firing rate that is seen on all trials regardless of motion strength and direction.”

Some principles gleaned from simple binary decisions are likely to extend to decisions with more than 2 choices.

“Our study suggests that some of the principles gleaned from simple binary decisions are likely to extend to decisions with more than 2 choices.”

The effect of motion strength on buildup rate is not explained by averaging over different proportions of correct and error trials.

“Importantly, however, it demonstrates that the effect of motion strength on buildup rate is not explained by averaging over different proportions of correct and error trials.”

• Also stated in: § Supplementary Materials · boosted

  “it demonstrates that the effect of motion strength on buildup rate is not explained by averaging over different proportions of correct and error trials.”

The oppositional relationship between LIP neurons tuned to opposing motion directions was demonstrated directly by stimulating MT neurons and measuring the effect on choice and reaction time.

“This oppositional relationship was demonstrated directly by stimulating MT neurons and measuring the effect on choice and RT.”

In the framework of bounded accumulation, the time-dependent rise causes decisions to terminate as time elapses, regardless of the evidence.

“in the framework of bounded accumulation 17, it causes decisions to terminate as time elapses, regardless of the evidence.”

• cites [17] Reddi, B.A. & Carpenter, R.H. The influence of urgency on decision time. Nat. Neurosci. 3, 827–830 (2000). sourceNot checked yet

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The lower starting point implies a larger excursion in firing rate from start to end of the decision.

“Thus the lower starting point implies a larger excursion in firing rate from start to end of the decision.”

There is an inverse relationship between the number of possible eye movement directions and firing rates in the superior colliculus preceding a saccade instruction.

“A major difference between 2- and 4-choice responses was the firing rate at the beginning of the decision process (Fig. 3), consistent with the inverse relationship between the number of possible eye movement directions and firing rates in the superior colliculus preceding a saccade instruction 30.”

• cites [30] Basso, M.A. & Wurtz, R.H. Modulation of neuronal activity in superior colliculus by changes in target probability. J. Neurosci. 18, 7519–7534 (1998). sourceNot checked yet

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The stronger urgency in the 2-choice conditions amplifies the effective difference in excursion between conditions because it effectively shrinks the excursion: less of the range of LIP firing rates between start and end is used to represent accumulated evidence.

“This amplifies the effective difference in excursion between the conditions because it effectively shrinks the excursion: less of the range of LIP firing rates between start and end is used to represent the accumulated evidence.”

The reduction in firing rate on the 4-choice task is unlikely to be due to a low-level factor such as the presence of a target in the neuron's inhibitory surround.

“We think the reduction in firing rate on 4-choice is unlikely to be due to a low-level factor, such as the presence of a target in the neuron’s inhibitory surround.”

The graphs support the existence of a bound in firing rate that marks the termination of trials.

“The graphs support the existence of a bound in firing rate that marks the termination of trials.”

• Also stated in: § Supplementary Materials · plain

  “The graphs support the existence of a bound in firing rate that marks the termination of trials.”

When human subjects perform the 2-choice motion task, they appear to adjust the bound (or excursion) when they trade off speed and accuracy.

“When human subjects perform the 2-choice motion task, they appear to adjust the bound (or excursion) when they trade off speed and accuracy3.”

• cites [3] Palmer, J., Huk, A.C. & Shadlen, M.N. The effect of stimulus strength on the speed and accuracy of a perceptual decision. J. Vis. 5, 376–404 (2005). sourceNot checked yet

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Our easy set of motion strengths rendered fast decisions less costly in the 2-choice task.

“Here, however, our easy set of motion strengths rendered fast decisions less costly in the 2-choice task.”

No inhibitory surround is seen in LIP receptive fields.

“First, no inhibitory surround is seen in LIP RFs 31,32.”

• cites [31] Platt, M.L. & Glimcher, P.W. Response fields of intraparietal neurons quantified with multiple saccadic targets. Exp. Brain Res. 121, 65–75 (1998). sourceNot checked yet

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• cites [32] Ben Hamed, S., Duhamel, J.R., Bremmer, F. & Graf, W. Visual receptive field modulation in the lateral intraparietal area during attentive fixation and free gaze. Cereb. Cortex 12, 234–245 (2002). sourceNot checked yet

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In the 4-choice task, the lower firing rate at the decision's beginning confers a higher bound for terminating the decision.

“In our 4-choice task, this lower firing rate at the decision’s beginning confers a higher bound for terminating the decision.”

The computation that LIP performs on the motion signals it receives from MT (and elsewhere) is similar in the 2- and 4-choice tasks.

“Our results suggest that the computation that LIP performs on the motion signals it receives from MT (and elsewhere) is similar in the 2- and 4-choice tasks.”

According to the bounded accumulation model, the longer RT on errors arises as a consequence of the urgency signal u(t), which imposes a more lax criterion for terminating the decision, thereby rendering errors more frequent.

“According to the model, the longer RT on errors arises as a consequence of the urgency signal, u(t), which effectively imposes a more lax criterion for terminating the decision (as if the bound were dropping as a function of time), thereby rendering errors more frequent36.”

• cites [36] Ditterich, J. Stochastic models of decisions about motion direction: behavior and physiology. Neural Netw. 19, 981–1012 (2006). sourceNot checked yet

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• AssumptionThe authors state this as an assumption: Direction sensors with orthogonal preferences do not contribute substantially to the mean accumulation.
• AssumptionThe authors state this as an assumption: For decisions between 2 opposite directions, the momentary evidence is a difference in firing rates of direction selective neurons with opposite direction preferences.

The observed bound on accumulation ties together in a single mechanism the content of a decision with the time required to make it.

“In addition, the observed bound on the accumulation ties together in a single mechanism the content of a decision with the time required to make it.”

The bounded accumulation model explains the RTs measured on error trials.

“The bounded accumulation model explains the RTs measured on error trials.”

• AssumptionThe authors state this as an assumption: Direction sensors with orthogonal preferences do not contribute substantially to the mean accumulation.
• AssumptionThe authors state this as an assumption: For decisions between 2 opposite directions, the momentary evidence is a difference in firing rates of direction selective neurons with opposite direction preferences.

This rules out the possibility that the difference in excursion was compensated by a change in the scaling of accumulated evidence into units of LIP firing rate.

“This rules out the possibility that the difference in excursion was compensated by a change in the scaling of accumulated evidence into units of LIP firing rate.”

In the framework of bounded accumulation, a larger excursion improves signal to noise at decision termination-or equivalently, reduces uncertainty-at the expense of decision time.

“In the framework of bounded accumulation, a larger excursion improves signal to noise at decision termination—or equivalently, reduces uncertainty—at the expense of decision time.”

In the two-choice task, LIP neurons seem to reflect the difference in firing rates between neurons tuned to two opposing directions of motion.

“In the two-choice task, LIP neurons seem to reflect the difference in firing rates between neurons tuned to two opposing directions of motion21.”

• cites [21] Ditterich, J., Mazurek, M.E. & Shadlen, M.N. Microstimulation of visual cortex affects the speed of perceptual decisions. Nat. Neurosci. 6, 891–898 (2003). sourceNot checked yet

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In the 4-choice task, time is costly.

“In the 4-choice task, time is costly.”

The urgency signal is an essential feature of the model used to explain choice and reaction time in these experiments.

“It is an essential feature of the model used to explain choice and RT in these experiments.”

No reliable choice bias was found on 0% coherence motion trials in the 2-, 4-, and 90° control tasks.

“No reliable bias was found. For 2-choice trials, the number of Tin and Tout choices was 1452 vs. 1387 (p=0.22, Binomial distribution, H0:p = 0.5). For 4-choice trials, the number of Tin, Tout, T+90, and T−9 was 1461, 1421, 1387, and 1426 (p=0.65, χ2 test, H0: equal proportions).”

• Also stated in: § Supplementary Material · plain

  “because the monkeys were unbiased in their choices on these trials in all three tasks.”

The similarity of mean responses to T90 and Tout targets suggests that T90 targets are not in a suppressive region of the RF or its surround.

“suggesting that they are not in a suppressive region of the RF or its surround.”