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Reward sharpens orientation coding independently of attention.

Baldassi S, Simoncini C - Front Neurosci (2011)

Bottom Line: However it is unclear whether this is due to high level modulations in the output modules of associated neural systems or due to low level mechanisms favoring more "generous" inputs?We found that reward, at any rate, improved performance.However, higher reward rates showed an improvement of orientation discrimination thresholds by about 50% across conditions and sharpened behavioral tuning functions.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, University of Florence Florence, Italy.

ABSTRACT
It has long been known that rewarding improves performance. However it is unclear whether this is due to high level modulations in the output modules of associated neural systems or due to low level mechanisms favoring more "generous" inputs? Some recent studies suggest that primary sensory areas, including V1 and A1, may form part of the circuitry of reward-based modulations, but there is no data indicating whether reward can be dissociated from attention or cross-trial forms of perceptual learning. Here we address this issue with a psychophysical dual task, to control attention, while perceptual performance on oriented targets associated with different levels of reward is assessed by measuring both orientation discrimination thresholds and behavioral tuning functions for tilt values near threshold. We found that reward, at any rate, improved performance. However, higher reward rates showed an improvement of orientation discrimination thresholds by about 50% across conditions and sharpened behavioral tuning functions. Data were unaffected by changing the attentional load and by dissociating the feature of the reward cue from the task-relevant feature. These results suggest that reward may act within the span of a single trial independently of attention by modulating the activity of early sensory stages through a improvement of the signal-to-noise ratio of task-relevant channels.

No MeSH data available.


Related in: MedlinePlus

Average orientation discrimination thresholds (N = 4), corresponding to the 75% correct point of the psychometric function. The points represent the different reward rates (LRP, gray, and HRP, black) and different symbols represent different attentional conditions (light load, circles; heavy load, squares; X-cue, crossed squares). The straight horizontal lines marks the average orientation discrimination threshold for the peripheral target alone in the absence of attentional loading task (gray line, bottom) and for the dual task without reward (black line, top). Plotted data include only the analysis of trials in which the central task was successful (accurate counting). Error bars plot the SEM. The order of conditions (blocks) was shuffled throughout the experiment for all but the Heavy Load condition, executed later as a control experiment, which explains the slight (but not significant) reduction of thresholds (that leaves the pattern of results unaffected). Rewarding correct orientation discrimination responses, though as rarely as in 10% of the cases, sets performance of the main tasks to a level comparable to when there was no central task, whereas highly frequent rewards show an additional advantage of the same magnitude (about a factor of 1.5, p < 0.01). In the presence of an X-like cue thresholds are slightly higher for both reward rates, which may be due to a sub-optimal use of the cue. Importantly, the modulation of performance obtained by increasing the reward probability is of the same amount across attentional load sand cue types, suggesting that the effect cannot be explained by the use of spare attentional resources allocated to the peripheral task. Notice that the absolute value of threshold is high as discrimination is performed around the oblique axes, where orientation coding is rougher (Campbell et al., 1966).
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Figure 2: Average orientation discrimination thresholds (N = 4), corresponding to the 75% correct point of the psychometric function. The points represent the different reward rates (LRP, gray, and HRP, black) and different symbols represent different attentional conditions (light load, circles; heavy load, squares; X-cue, crossed squares). The straight horizontal lines marks the average orientation discrimination threshold for the peripheral target alone in the absence of attentional loading task (gray line, bottom) and for the dual task without reward (black line, top). Plotted data include only the analysis of trials in which the central task was successful (accurate counting). Error bars plot the SEM. The order of conditions (blocks) was shuffled throughout the experiment for all but the Heavy Load condition, executed later as a control experiment, which explains the slight (but not significant) reduction of thresholds (that leaves the pattern of results unaffected). Rewarding correct orientation discrimination responses, though as rarely as in 10% of the cases, sets performance of the main tasks to a level comparable to when there was no central task, whereas highly frequent rewards show an additional advantage of the same magnitude (about a factor of 1.5, p < 0.01). In the presence of an X-like cue thresholds are slightly higher for both reward rates, which may be due to a sub-optimal use of the cue. Importantly, the modulation of performance obtained by increasing the reward probability is of the same amount across attentional load sand cue types, suggesting that the effect cannot be explained by the use of spare attentional resources allocated to the peripheral task. Notice that the absolute value of threshold is high as discrimination is performed around the oblique axes, where orientation coding is rougher (Campbell et al., 1966).

Mentions: We measured orientation discrimination thresholds and behavioral tuning functions for three reward levels, two attentional load levels and two different reward cues. Figure 2 shows average thresholds, i.e., the orientation offset leading to 75% of correct discrimination responses, for the two types of trials, LRP (left gray points) and LRP (right black points), for the two attentional conditions, LL (circles) and HL (squares), and for the two type of cues, single line (filled symbols) and X-like cue (crossed squares). The two horizontal lines plot average thresholds the peripheral target was displayed without the counting task (lower gray line) and with the dual task but without reward (upper black line) and provide the basic demonstration that the two tasks used here share the same, limited-capacity system (t-test; p < 0.001). In all conditions orientation acuity was larger than in standard studies of orientation discrimination, where they typically span around 1–2° (see also the feature-independent cue experiment below). This is simply due to the fact that the reference axes for the discrimination were tilted by 45°, reflecting the so-called oblique effect (Campbell et al., 1966), i.e., a rougher and noisier encoding of orientation relative to the horizontal and the vertical axis. All the reward rates, load conditions, and cue types showed significantly lower orientation discrimination thresholds than for the dual task without reward (black horizontal line) that were of about 9°. However, in the presence of reward, average thresholds decreased substantially, spanning from about 8°–6° for LRP trials to about 4°–3° for HRP trials (Figure 2, left vs. right points). It is noticeable that introducing reward to the task, even in 10% of the trials, reduced thresholds substantially, but it is even more surprising that when the reward probability was as high as 90%, perceptual performance was lower than for the peripheral task alone (lower gray horizontal line) for both the LL and the HL condition. Again, differential learning cannot adequately explain these results as all the conditions (except the HL condition that was ran later, as a separate control experiment) were executed in the same block or in different blocks interleaved across conditions. Comparing the two reward rates of our experiment, orientation discrimination thresholds in LRP trials were about 50% higher than in HRP trials (t-test; p < 0.01 for LL and X-cue; p < 0.001 for HL). This difference was not affected by the attentional load devoted to the central counting task, as shown by the parallel functions of Figure 2, suggesting that the difference between reward rates could not be attributed to spare attentional resources allocated peripherally in the HRP condition. Indeed, the counting performance did not depend at all on the reward rate, which remained stable at about 95% in the LL and 55% in the HL condition for both the LRP and HRP condition (t-test; p = 0.769), ruling out the possibility of response shifts a posteriori. Importantly, the 55% rate of correct counting shown in the HL, dual task coincided with the preliminary measures that we took in each observer for the counting task alone, in the absence of peripheral task, implying that this was an absolute limit introduced by the task and that the peripheral task did not shift resources, as otherwise counting performance should have worsened in the dual task. It is noteworthy that this effect was obtained when the reference axis of the peripheral target was tilted in the same direction of the cue, and that it worked also when the orthogonal axis (signaling a LRP trial) was physically part of the cue, in the X-like control experiment. This suggests that the higher likelihood of achieving a reward improved the representation of the cued axes according to a top-down mechanism.


Reward sharpens orientation coding independently of attention.

Baldassi S, Simoncini C - Front Neurosci (2011)

Average orientation discrimination thresholds (N = 4), corresponding to the 75% correct point of the psychometric function. The points represent the different reward rates (LRP, gray, and HRP, black) and different symbols represent different attentional conditions (light load, circles; heavy load, squares; X-cue, crossed squares). The straight horizontal lines marks the average orientation discrimination threshold for the peripheral target alone in the absence of attentional loading task (gray line, bottom) and for the dual task without reward (black line, top). Plotted data include only the analysis of trials in which the central task was successful (accurate counting). Error bars plot the SEM. The order of conditions (blocks) was shuffled throughout the experiment for all but the Heavy Load condition, executed later as a control experiment, which explains the slight (but not significant) reduction of thresholds (that leaves the pattern of results unaffected). Rewarding correct orientation discrimination responses, though as rarely as in 10% of the cases, sets performance of the main tasks to a level comparable to when there was no central task, whereas highly frequent rewards show an additional advantage of the same magnitude (about a factor of 1.5, p < 0.01). In the presence of an X-like cue thresholds are slightly higher for both reward rates, which may be due to a sub-optimal use of the cue. Importantly, the modulation of performance obtained by increasing the reward probability is of the same amount across attentional load sand cue types, suggesting that the effect cannot be explained by the use of spare attentional resources allocated to the peripheral task. Notice that the absolute value of threshold is high as discrimination is performed around the oblique axes, where orientation coding is rougher (Campbell et al., 1966).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3037789&req=5

Figure 2: Average orientation discrimination thresholds (N = 4), corresponding to the 75% correct point of the psychometric function. The points represent the different reward rates (LRP, gray, and HRP, black) and different symbols represent different attentional conditions (light load, circles; heavy load, squares; X-cue, crossed squares). The straight horizontal lines marks the average orientation discrimination threshold for the peripheral target alone in the absence of attentional loading task (gray line, bottom) and for the dual task without reward (black line, top). Plotted data include only the analysis of trials in which the central task was successful (accurate counting). Error bars plot the SEM. The order of conditions (blocks) was shuffled throughout the experiment for all but the Heavy Load condition, executed later as a control experiment, which explains the slight (but not significant) reduction of thresholds (that leaves the pattern of results unaffected). Rewarding correct orientation discrimination responses, though as rarely as in 10% of the cases, sets performance of the main tasks to a level comparable to when there was no central task, whereas highly frequent rewards show an additional advantage of the same magnitude (about a factor of 1.5, p < 0.01). In the presence of an X-like cue thresholds are slightly higher for both reward rates, which may be due to a sub-optimal use of the cue. Importantly, the modulation of performance obtained by increasing the reward probability is of the same amount across attentional load sand cue types, suggesting that the effect cannot be explained by the use of spare attentional resources allocated to the peripheral task. Notice that the absolute value of threshold is high as discrimination is performed around the oblique axes, where orientation coding is rougher (Campbell et al., 1966).
Mentions: We measured orientation discrimination thresholds and behavioral tuning functions for three reward levels, two attentional load levels and two different reward cues. Figure 2 shows average thresholds, i.e., the orientation offset leading to 75% of correct discrimination responses, for the two types of trials, LRP (left gray points) and LRP (right black points), for the two attentional conditions, LL (circles) and HL (squares), and for the two type of cues, single line (filled symbols) and X-like cue (crossed squares). The two horizontal lines plot average thresholds the peripheral target was displayed without the counting task (lower gray line) and with the dual task but without reward (upper black line) and provide the basic demonstration that the two tasks used here share the same, limited-capacity system (t-test; p < 0.001). In all conditions orientation acuity was larger than in standard studies of orientation discrimination, where they typically span around 1–2° (see also the feature-independent cue experiment below). This is simply due to the fact that the reference axes for the discrimination were tilted by 45°, reflecting the so-called oblique effect (Campbell et al., 1966), i.e., a rougher and noisier encoding of orientation relative to the horizontal and the vertical axis. All the reward rates, load conditions, and cue types showed significantly lower orientation discrimination thresholds than for the dual task without reward (black horizontal line) that were of about 9°. However, in the presence of reward, average thresholds decreased substantially, spanning from about 8°–6° for LRP trials to about 4°–3° for HRP trials (Figure 2, left vs. right points). It is noticeable that introducing reward to the task, even in 10% of the trials, reduced thresholds substantially, but it is even more surprising that when the reward probability was as high as 90%, perceptual performance was lower than for the peripheral task alone (lower gray horizontal line) for both the LL and the HL condition. Again, differential learning cannot adequately explain these results as all the conditions (except the HL condition that was ran later, as a separate control experiment) were executed in the same block or in different blocks interleaved across conditions. Comparing the two reward rates of our experiment, orientation discrimination thresholds in LRP trials were about 50% higher than in HRP trials (t-test; p < 0.01 for LL and X-cue; p < 0.001 for HL). This difference was not affected by the attentional load devoted to the central counting task, as shown by the parallel functions of Figure 2, suggesting that the difference between reward rates could not be attributed to spare attentional resources allocated peripherally in the HRP condition. Indeed, the counting performance did not depend at all on the reward rate, which remained stable at about 95% in the LL and 55% in the HL condition for both the LRP and HRP condition (t-test; p = 0.769), ruling out the possibility of response shifts a posteriori. Importantly, the 55% rate of correct counting shown in the HL, dual task coincided with the preliminary measures that we took in each observer for the counting task alone, in the absence of peripheral task, implying that this was an absolute limit introduced by the task and that the peripheral task did not shift resources, as otherwise counting performance should have worsened in the dual task. It is noteworthy that this effect was obtained when the reference axis of the peripheral target was tilted in the same direction of the cue, and that it worked also when the orthogonal axis (signaling a LRP trial) was physically part of the cue, in the X-like control experiment. This suggests that the higher likelihood of achieving a reward improved the representation of the cued axes according to a top-down mechanism.

Bottom Line: However it is unclear whether this is due to high level modulations in the output modules of associated neural systems or due to low level mechanisms favoring more "generous" inputs?We found that reward, at any rate, improved performance.However, higher reward rates showed an improvement of orientation discrimination thresholds by about 50% across conditions and sharpened behavioral tuning functions.

View Article: PubMed Central - PubMed

Affiliation: Department of Psychology, University of Florence Florence, Italy.

ABSTRACT
It has long been known that rewarding improves performance. However it is unclear whether this is due to high level modulations in the output modules of associated neural systems or due to low level mechanisms favoring more "generous" inputs? Some recent studies suggest that primary sensory areas, including V1 and A1, may form part of the circuitry of reward-based modulations, but there is no data indicating whether reward can be dissociated from attention or cross-trial forms of perceptual learning. Here we address this issue with a psychophysical dual task, to control attention, while perceptual performance on oriented targets associated with different levels of reward is assessed by measuring both orientation discrimination thresholds and behavioral tuning functions for tilt values near threshold. We found that reward, at any rate, improved performance. However, higher reward rates showed an improvement of orientation discrimination thresholds by about 50% across conditions and sharpened behavioral tuning functions. Data were unaffected by changing the attentional load and by dissociating the feature of the reward cue from the task-relevant feature. These results suggest that reward may act within the span of a single trial independently of attention by modulating the activity of early sensory stages through a improvement of the signal-to-noise ratio of task-relevant channels.

No MeSH data available.


Related in: MedlinePlus