Bounded Integration in Parietal Cortex Underlies Decisions Even When Viewing Duration Is Dictated by the Environment

Monkeys performing a direction discrimination task commit to a choice when the accumulated evidence reaches a threshold level (or bound), sometimes long before the end of the stimulus.

“Contrary to these assumptions, we show that monkeys performing a direction discrimination task commit to a choice when the accumulated evidence reaches a threshold level (or bound), sometimes long before the end of stimulus.”

• Also stated in: § Results · plain

  “We show that bounded accumulation of evidence explains the performance on this task.”

Bounded accumulation of evidence is reflected in the activity of neurons in the lateral intraparietal cortex.

“This bounded accumulation of evidence is reflected in the activity of neurons in the lateral intraparietal cortex.”

Termination of a decision process, while the stimulus remains visible, delimits the improvement in performance that might otherwise accrue with prolonged stimulus exposures.

“Additionally, we show that termination of a decision process, while the stimulus remains visible, delimits the improvement in performance that might otherwise accrue with prolonged stimulus exposures (Burr and Santoro, 2001).”

For short-duration stimuli, the mean reaction time from the Go signal was 272.9 ± 0.6 ms.

“For the short-duration stimuli, the mean RT from the Go signal was 272.9 Ϯ 0.6 ms.”

In this study, both challenges are met in a simple perceptual decision about motion direction.

“In this study, we show that both of these challenges are met in a simple perceptual decision about motion direction.”

• AssumptionRests on an assumption: When a behavioral response is solicited by an exogenous cue or instruction, there can be a discrepancy between the time of response and commitment to a choice.

Differences in mean responses of individual neurons do not achieve a common statistical criterion until 257 ± 9 ms after motion onset.

“the differences in mean responses of individual neurons do not achieve a common statistical criterion until 257 Ϯ 9 ms after motion onset (t test; p Ͻ 0.05).”

There is no inherent effect of pulse time independent of pulse direction.

“␣ 3 was indistinguishable from 0 (Ϫ0.12Ϯ 0.19; p ϭ 0.26), indicating no inherent effect of pulse time independent of pulse direction.”

Similar patterns are apparent in the motion energy profiles of shorter-duration trials and in the motion energy profiles of trials with >0% coherence.

“Similar patterns are apparent in the motion energy profiles of shorter-duration trials and in the motion energy profiles of trials with Ͼ0% coherence (data not shown).”

The maximum likelihood fit places the transition point at n = 15, corresponding to stimulus durations 403-443 ms (mean, 420 ms).

“The maximum likelihood fit places the transition point at n ϭ 15, which corresponds to stimulus durations 403-443 ms (mean, 420 ms).”

For trials with stimulus durations of 700 ms or more, the firing rates were overlapping (slope change -6.6 ± 19.0 spikes/s^2; p = 0.37).

“Similarly, the firing rates were overlapping for trials with stimulus durations of 700 ms or more (Fig. 6C) (slope change, Ϫ6.6 Ϯ 19.0 spikes/s 2 ; p ϭ 0.37).”

The motion pulses were more effective when they were presented earlier in the trial.

“Importantly, these pulses were more effective when they were presented earlier in the trial.”

The motion pulses significantly biased the monkey's choice toward the pulse direction (psychometric function shift across all trials, 1.3 ± 0.1% coherence; p < 10^-8).

“The motion pulses significantly biased the monkey's choice toward the pulse direction (Fig. 5A) (psychometric function shift across all trials, 1.3 Ϯ 0.1% coherence; p Ͻ 10 Ϫ8 )”

The bias caused by late pulses was indistinguishable from 0 (third quartile shift 0.2 ± 0.4%, p = 0.26; fourth quartile shift -0.1 ± 0.4%, p = 0.63).

“the bias caused by the late pulses was indistinguishable from 0 (third quartile: shift, 0.2 Ϯ 0.4%, p ϭ 0.26; fourth quartile: shift, Ϫ0.1 Ϯ 0.4%, p ϭ 0.63).”

The increase in input variance was first evident 207 ± 13 ms after motion onset.

“This increase in input variance was first evident 207 Ϯ 13 ms after the motion onset.”

The buildup rate of neural activity was significantly larger for trials in which the monkey responded faster (slope change 48.7 ± 21.3 spikes/s^2; p = 0.02).

“The buildup rate of neural activity was significantly larger for the trials in which the monkey responded faster (Fig. 6 A) (slope change, 48.7 Ϯ 21.3 spikes/s 2 ; p ϭ 0.02).”

For short-duration delay trials, the firing rates of short- and long-RT trials essentially overlapped from the beginning of the accumulation process (slope change -17.4 ± 18.2 spikes/s^2; p = 0.18).

“For short-duration trials (Ͻ200 ms) in which a 500 -1000 ms delay period was introduced before the Go signal (i.e., delay trials), the firing rate of the short-and long-RT trials essentially overlapped from the beginning of the accumulation process (Fig. 6 B) (slope change, Ϫ17.4 Ϯ 18.2 spikes/s 2 ; p ϭ 0.18).”

The central tendency of response times on short-duration trials is 150-200 ms after the emergence of the decision build up in LIP.

“This is 150 -200 ms after the emergence of the decision build up in LIP.”

Motion pulses cause a significant choice bias.

“Also, ␣ 2 is significantly larger than 0 (1.51 Ϯ 0.52; p ϭ 0.002), compatible with the results of Equation 4.”

Discrimination thresholds were similar for delay and no-delay trials.

“The discrimination thresholds were similar for delay and no-delay trials.”

The same set of stimuli, matched for coherence and exposure duration, gave rise to much faster responses on trials incorporating a delay period after the stimulus.

“the same set of stimuli, matched for coherence and exposure duration, gave rise to much faster responses on trials incorporating a delay period after the stimulus.”

Discrimination threshold decreased (sensitivity increased) when the monkeys were provided longer viewing durations.

“Figure 3B shows a clear decrease in discrimination threshold (i.e., an increase in sensitivity) when the monkeys were provided longer viewing durations.”

The distribution of response times on short-duration trials has its central tendency almost 400 ms after stimulus onset (mean 393 ± 0.7 ms; interquartile range 366-413 ms).

“The distribution shown in Figure 2C has its central tendency almost 400 ms after stimulus onset (mean, 393 Ϯ 0.7 ms; interquartile range, 366 -413 ms).”

The effect of motion pulses on choice bias diminishes for later pulses.

“This value was significantly negative (␣ 4 ϭ Ϫ0.40 Ϯ 0.19) indicating a diminishing effect for later pulses.”

On short-duration motion trials, eye movements were initiated only after a relatively long latency.

“Although the motion was brief, the eye movements were initiated only after a relatively long latency.”

Early pulses caused significantly larger biases than late ones (p = 0.018).

“the early pulses caused significantly larger biases than the late ones (Fig. 5B) ( p ϭ 0.018)”

Motion strength did not affect the correlation between bound-crossing time and reaction time.

“No other terms were significant in the analysis ( p Ն 0.1), indicating that motion strength did not affect the correlation.”

Baseline firing rate did not affect reaction time for any coherence level.

“Moreover, baseline firing rates did not affect RT ( p Ͼ 0.17; H 0 : ␤ 3 ϭ 0) for any coherence level.”

The data are only partly consistent with the prediction of perfect accumulation.

“The data, however, are only partly consistent with this prediction.”

• AssumptionRests on an assumption: The stochastic motion stimulus produces a stream of evidence samples that are statistically independent over the time course of the trial.

A three-way ANOVA showed no significant effect of coherence or stimulus duration on sustained activity.

“A three-way ANOVA with coherence and duration as the fixed effects and the neurons as the random effect showed no significant effect for coherence (F (4,270) ϭ 1.07; p ϭ 0.37) or stimulus duration (F (1,58) ϭ 0.36; p ϭ 0.55).”

The correlation between bound-crossing time and reaction time remained significant when controlling for baseline firing rate.

“For all coherence levels, ␤ 2 remained significantly different from zero ( p Ͻ 0.01; H 0 : ␤ 2 ϭ 0).”

Firing rates associated with T_in and T_out choices begin to diverge more than 200 ms after motion onset.

“the firing rates associated with T in and T out choices begin to diverge Ͼ200 ms after motion onset”

• cites Kim and Shadlen, 1999Not checked yet

  Not checked in the free run.

• cites Roitman and Shadlen, 2002 sourceNot checked yet

  Not checked in the free run.

• cites Huk and Shadlen, 2005Not checked yet

  Not checked in the free run.

For 0% coherence trials with no delay and short stimulus durations (<200 ms), the monkey's RTs relative to the Go signal were positively correlated to decision times estimated from neural data (r = 0.16; p = 1.4 × 10^-4).

“For 0% coherence trials with no delay and short stimulus durations (Ͻ200 ms), the monkey's RTs relative to the Go signal were positively correlated to the decision times estimated from the neural data (Fig. 7A) (r ϭ 0.16; p ϭ 1.4 ϫ 10 Ϫ4 , Fisher z).”

• AssumptionThe authors state this as an assumption: The bound height for each neuron is near the level of firing rate that the neuron attains at the end of long-duration stimuli or during the delay period after the stimulus in delay trials.

The difference in buildup rate was not significant for delay trials with short stimulus durations (slope change -11.6 ± 29.6 spikes/s^2; p = 0.35).

“Similar to the correct trials, the difference in the buildup rate was not significant for delay trials with short stimulus durations (slope change, Ϫ11.6 Ϯ 29.6 spikes/s 2 ; p ϭ 0.35).”

The monkeys did not appear to lose, or leak away, information acquired at the beginning of the trial.

“They did not appear to lose, or leak away, information acquired at the beginning of the trial (Figs. 4, 5).”

The time from the estimated neural decision to saccade initiation was 94.4 ± 2.0 ms.

“The time from the estimated neural decision to saccade initiation was 94.4 Ϯ 2.0 ms (mean Ϯ SEM for all trials represented in Fig. 7 A, B).”

• AssumptionThe authors state this as an assumption: The bound height for each neuron is near the level of firing rate that the neuron attains at the end of long-duration stimuli or during the delay period after the stimulus in delay trials.

Inserting a delay period before the Go signal reduced the correlation between bound-crossing time and response time (p = 0.0005).

“Importantly, inserting a delay period before the Go signal reduced the correlation between the bound-crossing time and the response time (Fig. 7C,D) ( p ϭ 0.0005) (Eq.7).”

In delay trials, the correlation coefficients were not significantly different from 0.

“In fact, the correlation coefficients were not significantly different from 0.”

Time-limited accumulation fails to account for the changes of discrimination thresholds.

“the time-limited accumulation fails to account for the changes of discrimination thresholds (Fig. S1, available at www.jneurosci.org as supplemental material).”

The correlation remained significant for all coherence levels (p < 0.01).

“The correlation remained significant for all coherence levels ( p Ͻ 0.01).”

A weak positive correlation is evident on short-duration stimuli.

“A weak positive correlation is evident on short-duration stimuli.”

The rate of buildup for fast and slow errors greatly resembled the pattern observed with fast and slow correct choices.

“Moreover, the rate of buildup for fast and slow errors greatly resembled that of the pattern observed with fast and slow correct choices.”

The prediction that pulses remain effective at later times for weaker motion than for stronger motion is exactly what we observed.

“This is exactly what we observed (Fig. S2, available at www.jneurosci.org as supplemental material).”

The slopes of regression between the bound-crossing time and the monkey's response time are less than 1.

“the slopes of regression between the bound-crossing time and the monkey's response time are Ͻ1”

For short stimulus duration error trials without a delay period, the buildup rate of neural activity was significantly larger in trials in which the monkey responded faster (slope change 59.4 ± 31.2 spike/s^2; p = 0.05).

“For short stimulus duration trials (Ͻ200 ms) without a delay period, the buildup rate of neural activity was significantly larger in the trials in which the monkey responded faster (slope change, 59.4 Ϯ 31.2 spike/s 2 ; p ϭ 0.05).”

Despite the long latency for the representation of accumulated evidence in LIP, activity in this structure preceded the monkey's behavioral responses even for extremely short stimuli.

“despite the long latency for the representation of accumulated evidence in LIP, activity in this structure preceded the monkey's behavioral re- sponses even for extremely short stimuli.”

LIP neural responses begin to convey information about motion direction and choice after approximately 200 ms.

“The neural responses begin to convey information about motion direction and choice after ϳ200 ms.”

Perceptual accuracy improves only limitedly with longer motion viewing duration.

“Limited improvement in perceptual accuracy with longer motion viewing duration.”

The effect of motion information on decisions diminishes at longer viewing times.

“The effect of motion information on decisions diminishes at longer viewing times.”

Behavioral discrimination thresholds deviate from perfect accumulation for longer viewing duration.

“Behavioral discrimination thresholds deviate from perfect accumulation for longer viewing duration.”

The rise in neural response variance corresponds with accumulation of noisy evidence.

“The rise in neural response variance corresponds with accumulation of noisy evidence.”

The motion pulses significantly biased the monkey's choice toward their corresponding target.

“The motion pulses significantly biased the monkey's choice toward their corresponding target.”

Monkeys base their decisions on accumulation of evidence for much shorter durations than 2 s.

“However, as demonstrated here, monkeys base their decisions on accumulation of evidence for much shorter durations.”

A similar diminishing effect of viewing duration was observed in monkeys that were never trained on a reaction time task.

“we observed a similar diminishing effect of viewing duration in monkeys that were never trained on an RT task.”

The bias from motion pulses is equivalent to 1.3 ± 0.1% coherent motion.

“This bias is quantified by the horizontal separation of the two functions, here equivalent to 1.3 Ϯ 0.1% coherent motion.”

The input variance begins to increase reliably at the time indicated by the arrow.

“The arrow indicates when the input variance begins to increase reliably.”

Subjects limit sampling of information even when they are not engaged in reaction time tasks.

“We show that subjects behave in this way in our experiment”

There is a correlation between saccadic response times and neural bound crossing time (Tbc).

“Correlation between saccadic response times and the neural bound crossing time (T bc ).”

The representation of accumulated evidence in LIP is delayed by at least 100 ms compared with the activity of direction-selective neurons in the middle temporal area (MT).

“First, the representation of accumulated evidence in LIP is delayed by at least 100 ms compared with the activity of direction-selective neurons in the middle temporal area (MT) (Britten et al., 1996;Bair et al., 2002;Roitman and Shadlen, 2002;Osborne et al., 2004;Huk and Shadlen, 2005).”

• cites Britten et al., 1996Not checked yet

  Not checked in the free run.

• cites Bair et al., 2002 sourceNot checked yet

  Not checked in the free run.

• cites Roitman and Shadlen, 2002 sourceNot checked yet

  Not checked in the free run.

The finding overturns the long-held assumption that failure to benefit from the full stream of information is a sign of inefficient (leaky) integration.

“The finding overturns a long-held assumption that such failure is a sign of inefficient (leaky) integration”

The decision process may terminate when the accumulated information reaches a critical level, even when subjects are required to view the whole stimulus.

“We show instead that the decision process may terminate when the accumulated information reaches a critical level, even when subjects are required to view the whole stimulus.”

The readout of visual cortex embraces a termination rule to limit processing even when potentially useful information is available.

“Thus, the readout of visual cortex embraces a termination rule to limit processing even when potentially useful information is available.”

The accumulation-to-bound mechanism generalizes beyond simple reaction-time tasks.

“Hence, the accumulation-to-bound mechanism generalizes beyond simple RT tasks.”

The build up of activity in LIP represents an accumulation of evidence in favor of one or the other direction alternatives.

“The build up of activity in LIP represents an accumulation of evidence in favor of one or the other direction alternatives.”

The divergence of firing rates for T_in and T_out choices marks the beginning of formation of the decision variable represented in LIP.

“This divergence marks the beginning of the formation of the decision variable represented in LIP.”

The absence of a correlation between buildup rates and response times in delay and long-duration trials can be explained if the decision process has terminated before the Go instruction on these trials.

“The absence of a correlation between buildup rates and response times in Figure 6, B and C, can be explained if the decision process has terminated before the Go instruction on these trials.”

The preceding analysis suggests that the mechanism for decision making in long-duration trials resembles the type of bounded accumulation of evidence thought to explain speed and accuracy in choice-reaction time tasks.

“The preceding analysis suggests that the mechanism for decision making in longduration trials resembles the type of bounded accumulation of evidence that is thought to explain the speed and accuracy of decisions in choice-reaction time tasks”

• cites Ratcliff, 1980Not checked yet

  Not checked in the free run.

• cites Smith, 1988Not checked yet

  Not checked in the free run.

• cites Link, 1992Not checked yet

  Not checked in the free run.

Bounded accumulation explains the diminishing improvement in long-duration trials because it posits that information is simply ignored once the decision bound is attained.

“Thus, bounded accumulation explains the diminishing improvement in long-duration trials, because it posits that information is simply ignored once the decision bound is attained.”

The earliest point in time that LIP can be said to represent information bearing on the decision is about 207 ms after motion onset.

“It is the earliest point in time that LIP can be said to represent information bearing on the decision.”

The free parameters of the models were not chosen to fit the motion energy profiles depicted in Figure 4D.

“Importantly, the free parameters of the models were not chosen to fit the motion energy profiles depicted in Figure 4D.”

The entire range of response times for short trials relative to neural activity is compatible with a process that awaits the dissociation point in LIP activity before forming a decision.

“the entire range of response times for these short trials relative to the neural activity is compatible with a process that awaits the dissociation point in LIP activity before forming a decision”

For the trials comprising all three panels of Figure 6, decisions probably arose faster when LIP activity built up faster.

“For the trials comprising all three panels of Figure 6, decisions probably arose faster when LIP activity built up faster.”

The flat hazard rate associated with the truncated exponential distribution of random durations minimizes the monkey's ability to anticipate the end of the trial.

“The flat hazard rate associated with this distribution of random durations minimizes the monkey's ability to anticipate the end of the trial (Ghose and Maunsell, 2002;Janssen and Shadlen, 2005).”

• cites Ghose and Maunsell, 2002Not checked yet

  Not checked in the free run.

• cites Janssen and Shadlen, 2005Not checked yet

  Not checked in the free run.

The delayed representation of accumulated evidence in LIP poses a challenge to the role of LIP neurons in the formation of decisions on the motion task.

“The delayed representation of the accumulated evidence in LIP poses a challenge to the role of LIP neurons in the formation of decisions on the motion task.”

The traces in Figure 6B and C are overlapping because they are formed from a random collection of faster and slower decisions.

“The traces in Figure 6, B and C, are overlapping, because they are formed from a random collection of faster and slower decisions.”

The pattern of correlation for short-duration trials but not longer or delay trials is consistent with an accumulation-to-bound mechanism.

“This pattern is also consistent with an accumulation-to-bound mechanism (Mazurek et al., 2003).”

• cites Mazurek et al., 2003Not checked yet

  Not checked in the free run.

The present study shows that the putative neural correlate of a decision variable in LIP is represented in a time frame compatible with the timing of decisions.

“It shows that the putative neural correlate of a decision variable in LIP is represented in a time frame that is compatible with the timing of decisions.”

The pulse should remain effective at later times for weaker motion than for stronger motion.

“the pulse should remain effective at later times for weaker motion than for stronger motion.”

Whatever effect baseline activity may have on response time is exerted through changing the bound-crossing time.

“The analysis indicates that whatever effect the baseline activity may have on the response time is exerted through changing the bound-crossing time.”

Our findings rule out a much larger class of alternative models to bounded accumulation.

“our findings rule out a much larger class of alternative models.”

The bounded accumulation model predicts that the effectiveness of a pulse depends on both the time it is delivered and the strength of the motion that it perturbed.

“the bounded accumulation model predicts that the effectiveness of a pulse depends on both the time it is delivered and the strength of the motion that it perturbed.”

Alternatives to bounded accumulation fail to explain the LIP neural responses in our experiment because they predict no correlation between neural threshold crossing time and RT.

“they fail to explain the LIP neural responses in our experiment, because they predict no correlation between the neural threshold crossing time and RT.”

The finding that LIP activity preceded behavioral responses even for short stimuli is consistent with a recent microstimulation study supporting a causal role for LIP in the decision process on this task.

“The finding is consistent with a recent microstimulation study, which supports a causal role for LIP in the decision process on this task (Hanks et al., 2006).”

• cites Hanks et al., 2006Not checked yet

  Not checked in the free run.

All alternatives to bounded accumulation assert a testable prediction: a pulse delivered at a particular time should affect the decision process identically for all motion strengths.

“all the alternatives to bounded accumulation assert a testable prediction: a pulse delivered at a particular time should affect the decision process identically for all motion strengths.”

The observed weak trial-by-trial correlations between neural activity and decisions are probably explained by the tendency of neurons with similar response characteristics (in this case, RFs) to covary in their variable discharge.

“the observed correlations are probably explained by the tendency of neurons with similar response characteristics (in this case, RFs) to covary in their variable discharge (Zohary et al., 1994;Shadlen et al., 1996;Parker and Newsome, 1998;Pezaris et al., 1999).”

• cites Zohary et al., 1994Not checked yet

  Not checked in the free run.

• cites Shadlen et al., 1996 sourceNot checked yet

  Not checked in the free run.

• cites Parker and Newsome, 1998Not checked yet

  Not checked in the free run.

• AssumptionRests on an assumption: Behavior is controlled by many neurons, and estimates of bound-crossing times from a single neuron in each trial are highly variable.

The lack of correlation in delay trials rules out potentially trivial explanations for the correlation such as increased vigilance, arousal, attentiveness, or level of preparedness.

“The lack of correlation in these trials also rules out potentially trivial explanations for the correlation such as increased vigilance, arousal, attentiveness, or level of preparedness.”

The improvement in accuracy was curtailed because the monkeys ignored information late in the trial.

“we determined that improvement was curtailed, because the monkeys ignored information late in the trial.”

The correlation was not explained by variations in baseline firing rates at the beginning of the trial.

“We also ensured that the correlation was not explained by variations in baseline firing rates at the beginning of the trial (see Materials and Methods,Eq. 8).”

Together, the analyses support the hypothesis that a bounded accumulation of evidence, represented in LIP activity, underlies the monkey's choices even when the stimulus duration is controlled by the environment.

“Together, these analyses (Figs.4567) support the hypothesis that a bounded accumulation of evidence, represented in LIP activity, underlies the monkey's choices even when the stimulus duration is controlled by the environment.”

For trials with fast neural bound crossings, the monkey's response time cannot decrease proportionally because it is limited by the motor preparation delay and the time needed to detect the Go signal.

“for trials with fast neural bound crossings, the monkey's response time cannot decrease proportionally, because it is limited by the motor preparation delay and the time needed to detect the Go signal.”

The present study shows that the decision process carries its own rule for termination even when the period in which evidence is available and the time for action are under the control of the environment.

“Also, it shows that the decision process carries its own rule for termination even when the period in which evidence is available and the time for action are under the control of the environment.”

A leaky accumulation process is not supported in this task.

“A leaky accumulation process, although theoretically capable of describing the observed curtailed improvement of accuracy (Usher and McClelland, 2001;Ratcliff and Smith, 2004;Busemeyer et al., 2006), is not supported in this task.”

• cites Usher and McClelland, 2001Not checked yet

  Not checked in the free run.

• cites Ratcliff and Smith, 2004Not checked yet

  Not checked in the free run.

• cites Busemeyer et al., 2006Not checked yet

  Not checked in the free run.

A fixed or predictable stimulus duration would allow subjects to start the decision process at times other than the beginning of the stimulus.

“In contrast to this approach, a stimulus duration that is fixed or predictable (Britten et al., 1993;Shadlen and Newsome, 2001;Parker et al., 2002;DeAngelis and Newsome, 2004;Krug, 2004;Krug et al., 2004;Uka and DeAngelis, 2004) would allow subjects to start the decision process at times other than the beginning of stimulus.”

• cites Britten et al., 1993Not checked yet

  Not checked in the free run.

• cites Shadlen and Newsome, 2001 sourceNot checked yet

  Not checked in the free run.

• cites Parker et al., 2002Not checked yet

  Not checked in the free run.

LIP appears to play a similar role whether the time course of evidence bearing on the decision is controlled by the subject or by the experimenter.

“LIP appears to play a similar role whether the time course of evidence bearing on the decision is controlled by the subject or by the experimenter.”

The variable RT in these trials is presumably explained by whatever mechanism accounts for variable motor latencies in the absence of a decision among alternatives.

“The variable RT in these trials is presumably explained by whatever mechanism accounts for variable motor latencies in the absence of a decision among alternatives (Carpenter, 1988;Hanes and Schall, 1996).”

• cites Carpenter, 1988Not checked yet

  Not checked in the free run.

• cites Hanes and Schall, 1996Not checked yet

  Not checked in the free run.

The accumulated evidence represented in LIP tends to plateau or saturate at the longer viewing durations used in previous experiments.

“It suggests that the accumulated evidence, represented in LIP, tends to plateau or saturate at the longer viewing durations used in previous experiments (Shadlen and Newsome, 2001).”

• cites Shadlen and Newsome, 2001 sourceNot checked yet

  Not checked in the free run.

The lack of correlation is expected because, according to the bounded accumulation hypothesis, the decision has completed long before the Go signal in these trials.

“The lack of correlation is expected, because, according to the bounded accumulation hypothesis, the decision has completed long before the Go signal in these trials.”

The brain simply ignores additional evidence that is available in the stimulus and in the firing of its sensory neurons.

“The similarity of the monkeys' performance on RT and fixed duration tasks (Roitman and Shadlen, 2002) adds further support to our contention that the brain simply ignores additional evidence that is available in the stimulus and in the firing of its sensory neurons.”

• cites Roitman and Shadlen, 2002 sourceNot checked yet

  Not checked in the free run.

The hypothesis unifies the decision mechanisms used in reaction time and non-reaction time tasks.

“Our hypothesis unifies the decision mechanisms used in RT and non-RT tasks.”

The use of a termination rule is not a consequence of training.

“The use of a termination rule is not a consequence of training”

Temporal smear across different trials could lead to the incorrect conclusion that subjects use information throughout the whole stimulus presentation.

“Such temporal smear across different trials could lead to the incorrect conclusion that subjects use the information throughout the whole stimulus presentation.”

One answer to why subjects make decisions based on a fraction of available information may be the concept of sampling cost.

“One answer may be the important, but often overlooked, concept of the sampling cost.”

• AssumptionRests on an assumption: Collecting evidence for reaching a decision consumes limited mental resources and retards engagement in other decisions or cognitive functions.

When sampling of information is costly, the brain must strike a balance between the amount of collected information and the improvement of accuracy.

“When sampling of information is costly, the brain must strike a balance between the amount of collected information and the improvement of accuracy.”

• AssumptionRests on an assumption: Collecting evidence for reaching a decision consumes limited mental resources and retards engagement in other decisions or cognitive functions.

Calculation of choice probability over long stimulus presentations mixes the relevant and irrelevant periods and leads to underestimation.

“Calculation of choice probability over long stimulus presentations mixes the relevant and irrelevant periods and leads to underestimation.”

Error responses are governed by the same mechanism as correct responses.

“Error responses are governed by the same mechanism as the correct responses.”

The relationship between trial-to-trial variability in the firing rate of sensory neurons and behavioral choices (choice probability) varies for relevant and irrelevant periods of neural responses.

“Similarly, the relationship between trialto-trial variability in the firing rate of sensory neurons and behavioral choices [choice probability (Britten et al., 1996;Parker and Newsome, 1998)] varies for relevant and irrelevant periods of neural responses.”

• cites Britten et al., 1996Not checked yet

  Not checked in the free run.

• cites Parker and Newsome, 1998Not checked yet

  Not checked in the free run.

When the experimenter or environment controls stimulus duration, the same considerations as in reaction time tasks appear to be in play, although decision time is covert.

“However, when the experimenter (or the environment) controls the stimulus duration, the same considerations appear to be in play, although the decision time is covert.”

• AssumptionRests on an assumption: The bound on evidence establishes the trade-off between accuracy and speed of decisions.

A mechanism to detect absorption to the attractor state is indispensable, particularly for reaction time tasks and for the short-duration trials in the current task.

“Such a mechanism is indispensable, particularly for reaction time tasks and for the short-duration trials in the task described in the current paper.”

The mechanism underlying the behavior is bounded accumulation of evidence, based on behavioral and neural data.

“we suggest a mechanism, bounded accumulation of evidence, based on behavioral and neural data.”