Introduction

In the spatial negative priming (SNP) tasks of interest, a visual target and/or distractor event are presented centrally (Buckolz, Fitzgeorge, & Knowles, 2012b) in trial pairs; first the prime, then the probe. Responding to a probe trial target’s position takes longer when it appears at a location previously occupied by the prime distractor (i.e., an ignored-repetition [IR] trial), compared with when it arises at a formerly unoccupied prime location (i.e., a control trial) (Milliken, Tipper, Houghton, & Lupianez, 2000; Neill, Terry, & Valdes, 1994). This latency imbalance is the most common index of SNP.

One recent explanation of SNP contends that the processing associated with distractor-occupied prime trial positions excludes the inhibition of the location itself, while including the activation (A) and subsequent inhibition (I) of the distractor location’s assigned response (Buckolz, Edgar, Kajaste, Lok, & Khan, 2012a; Guy, Buckolz, & Khan, 2006; Buckolz, Lok, Kajaste, Edgar, & Khan, 2014; Fitzgeorge, Buckolz, & Khan, 2011). This inhibition then renders the response to which it is applied execution resistant (ER).Footnote 1 Because a representation of prime-trial distractor processing is stored (Fitzgeorge & Buckolz, 2008; Haworth, Buckolz, & Kajaste, 2014), the distractor-response ER feature can be retrieved for the lifespan of this representation, when the probe trial is delivered. When a retrieved distractor response is required (either forced [ignored-repetition trials] or self-selected [free choice trials]; Fitzgeorge et al., 2011), its ER characteristic can influence later processing (collectively called, “inhibitory after-effects”).

Three inhibitory after-effects resulting from prime distractor response inhibition have been identified in location-based tasks. The first is the SNP effect itself. The required use of a prime distractor response on an ignored-repetition trial lengthens its reaction time, because it takes time to override its execution resistance (ER) feature. A second ER-induced inhibitory after-effect manifests itself when manual response error rates are higher for ignored-repetition than for control trials (Buckolz, Avramidis, & Fitzgeorge, 2008; Fitzgeorge & Buckolz, 2008). Presumably, this error imbalance arises, because efforts to override the ER feature of the distractor response on ignored-repetition trials are unsuccessful, necessarily producing a response selection error. A third inhibitory after-effect arises on free choice trials, where two permissible responses have been assigned to a single location. Subjects show a significant selection-bias against choosing a former distractor response when it competes against a control response (Fitzgeorge et al., 2011; Buckolz et al., 2014). The aversion to choosing the former distractor response presumably reflected its ER feature.

While the first two inhibitory after-effects noted above reflect an interference with task-appropriate target processing on ignored-repetition trials, a beneficial after-effect is possible. Specifically, the execution resistance (ER) feature of a just-inhibited prime distractor response should “protect” against its later erroneous production by repelling its selection (i.e., analogous to the ER repelling impact seen with free choice trials [Fitzgeorge et al., 2011]). Error protection evidence would see former distractor (ER-protected) responses used incorrectly less often than their control (nonprotected) counterparts on control probe trials.

Testing this error protection possibility was done here using both target-plus-distractor and target-only probe trials. With the target-plus-distractor probes, we assumed that a distractor-occupied location would activate and so provoke the execution of its assigned response (Fitzgeorge et al., 2011). Accordingly, four prime-probe trial Response Selection Error Categories were formed by crossing the execution resistance (ER) “protection” (yes/no) and the activation “provocation” (yes/no) factors (Scheme 1). All probe trial response selection errors arising when the probe target appeared at a new location can be placed into one of these four categories. Specifically, both “ER protection” and “provocation” can be absent, ER protection but not provocation can be present, provocation can occur without ER protection, and, finally, both protection and provocation can be present (Categories [1], [2], [3], and [4)], respectively; Scheme 1). Significantly smaller probe-trial error rates for Category [2] than for Category [1], and for Category [4] versus Category [3], would signal support for ER error protection. Moreover, the latter result would show that ER protection against faulty selection extends to former distractor responses that are urged into action by an external event (i.e., the probe distractor). Comparable error rates for Categories [4] and [2] would indicate that ER protection is equally effective whether its associated response is later externally provoked [4] or not [2] with probe arrival.

Scheme 1
scheme 1

Illustration of the four response selection error categories, formed by whether prime-probe trial paired responses include execution-resistance-induced error protection, and/or involve provocation, brought about by a probe distractor, respectively. All four categories apply to target-plus-distractor probe trials, while only categories [1] and [2] apply to target-only probe trials. ■ = distractor event. Probe target stimulus is not shown but it appears always at a location unoccupied on the prime trial

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Finally, we determined whether error protection remained effective over extensive practice with a repetitive task and hence represented a stable after-effect benefit. Longevity of execution resistance override duration (i.e., SNP) also was assessed. Existing SNP theories and data are largely silent on the longevity question (Buckolz et al., 2012b; Houghton & Tipper, 1994; Neill, 2007; Tipper, 2001).

Methods and participants

Thirty undergraduate students (15 males, 15 females), ranging in age from 20-25 years and with normal or corrected-to-normal vision, participated in this experiment.

Apparatus

The visual input display was presented in a dimly lit room on a 47.5-cm computer screen situated on a tabletop 73.5 cm above the floor. The display consisted of a centrally positioned fixation cross, accompanied on each side by two horizontal bar markers that served as locations for target (T) and/or distractor (D) presentations. These markers are denoted as L1-L4, going left to right. The fixation cross (0.9 cm in width) and the bar markers were white and appeared against a black background. Bar markers L2 and L3 were each located 2.4 cm, and L1 and L4 3.8 cm, from the fixation cross. Participants seated 196 cm from the display created a horizontal visual angle of about 2.2° for the bar markers. The to-be-responded-to target (green) and the to-be-ignored distractor (red) rectangles were the same size (0.9 cm wide and 1.9 cm high).

The keyboard responses of ‘D,’ ‘V,’ ‘L’, and ‘M’ were mapped onto their spatially compatible bar marker locations (L1, L2, L3, and L4) and were controlled by the middle and index fingers of the left and right hand.

Procedure

Trials were presented in pairs, first the prime and then the probe. A single target or a distractor event appeared with equal frequency on the prime trial, whereas the probe trial contained a target alone or a target plus a distractor.

All trials began with a 100 ms warning tone whose offset was immediately followed by the display configuration (bar markers and fixation cross), which remained on the screen for an entire prime-probe trial sequence (refer to Scheme 2 throughout). Two hundred milliseconds after the onset of the configuration, the prime-trial event, distractor or target, appeared for 157 ms. It was followed 700 ms later by the probe trial which contained a target plus a distractor or a target stimulus alone, and which again lasted for 157 ms. The execution of the probe-trial response, correct or incorrect, initiated an inter-trial duration of 1500 ms that culminated in the presentation of the warning tone and the next trial sequence.

Scheme 2
scheme 2

Illustration of the timing of events for a typical prime-probe trial sequence involving either a distractor-only [3A] or a target-only [3B] prime trial, followed either by a target-plus-distractor [5A] or a target-only [5B] probe trial. □ = to -be-responded to target event, ■ = to-be-ignored distractor event. IR = ignored-repetition trial, TR = target repetition trial

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Participants completed 14 Sessions consisting of 224 prime-probe trial pairs (total = 3,136 pairs); two Sessions per day of about 20 minutes each, separated by a rest of 10 minutes. Each Session contained an equal number of target-only and distractor-only events, with each of these events arising randomly and equally often at all of the four possible locations. On a subsequent probe trial, the target could appear alone (i.e., target-only, 57 %) or with a distractor (target + distractor, 43 %) event. With each of these trial types, the probe target appeared randomly and with equal frequency at all locations. For a given target location with the target + distractor probe trials, the distractor appeared unpredictably at each of the remaining locations. Governing the positioning of the prime and probe target and/or distractor events in this way precluded a contingency between prime trial and probe trial event placements, and gave rise to the following trial types for each Session.

Following the presentation of a prime trial distractor, there were 16 ignored-repetition and 48 Control trials (i.e., traditional Control trial is when no occupied prime location was reused on the probe trial) when the probe target appeared alone. When a distractor accompanied the probe target; 12 ignored-repetition and 24 traditional Control trials resulted, along with 12 additional trials, where the distractor reappeared at its prime location (i.e., distractor-repeat trial) [n = 112 prime-probe trial pairs]. When the prime trial contained only a target event, 16 target-repeat (prime target location is reused on the probe) and 48 Control trials resulted. When both a target and a distractor appeared on the probe trial; 12 target-repeat (distractor arose at a new location) and 24 Control trials were produced, along with 12 additional trials where the probe target appeared at a new location, while the distractor arose at the former target location (n = 112 trial pairs).

In addition to instructions needed to perform the task; participants were asked to avoid anticipations, to respond as quickly as possible while avoiding errors, and were informed that trials would be completed in pairs, each pair commencing with a beep. Before starting the experimental session, participants completed five practice trial pairs and had any questions answered to ensure task comprehension.

Results

Instances where button-press errors occurred on the prime and/or probe trials, along with occasions where response times were less than 100 ms (i.e., anticipations) or exceeded 900 ms (insufficient vigilance), were excluded from all latency analyses. Probe-trial data following target-only primes will not be discussed (Appendix A; Tables 1 and 2).

Probe-trial data (following distractor-only prime trials)

Response selection error protection

Button-press errors were classified according to whether the incorrect output had just served as a prime distractor or as a prime control response (i.e., had ER protection vs. no ER protection, respectively), and whether the response was currently associated with a probe distractor-occupied location or an empty probe-trial location (i.e., whether it had been provoked into action [activated] vs. not, respectively). This produced four prime-probe trial Categories (Scheme 1) for the target-plus-distractor probe trials but only two for the target-only probe trials, which lacked a provocation component (i.e., [1] & [2], Scheme 1). Probe-trial selection error rates attributable to each Category over Sessions for the target-plus-distractor and the target-only probe trials are found in Figs. 1 and 2, respectively.

Fig. 1
figure 1

Probe-trial response selection error percentages for target-plus-distractor probe trials as a function of Response Selection Error Category (Control: both prime and probe locations are empty; Protection: prime contains distractor, probe location is unoccupied; Provocation: prime location is empty, probe location contains a distractor; Both: both prime and probe locations contain a distractor [see Scheme 1]) and Sessions (224 prime-probe trial pairs/Session).

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Fig. 2
figure 2

Probe-trial response selection error percentages for the target-only probe trials as a function of Response Selection Error Category (Control: both prime and probe trial locations are unoccupied; Protection: prime location contains a distractor, probe location is unoccupied [see Scheme 1]) and Session (224 prime-probe trial pairs/Session).

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Button-press errors occurred on 4.0 % of the target-plus-distractor probe trials. An analysis of variance (ANOVA) was conducted using probe-trial button-press error percentages for each subject, and with Category ([1], [2], [3], & [4]; Scheme 1) and Sessions (1-14) serving as the main factors. Category produced the only significant effect, F(3, 87) = 72.72, p < 0.01, MSE = 1,483, (remaining F-values were < 1). Newman-Keuls tests (p < 0.05) applied to the Category main effect revealed that all pair-wise comparisons were significant. Error rates were most common for Category [1] 35.6 %, progressively declining thereafter for Categories [2] through [4]; 25.6 %, 7.27 %, and 1.03 %, respectively (Fig. 1).Footnote 2 Former distractor responses (Categories [2] & [4]) were used significantly less often in error than were their comparable counterparts (Categories [1] & [3], respectively). This includes when the response is activated by the presence of a probe distractor (distractor-response repeat trials, [3] > [4]). Overall, the effectiveness of the error protection attendant to former distractor responses on target-plus-distractor probe trials remained intact over practice.

The foregoing Category results were not replicated with target-only probe trials (Fig. 2), where button-press errors arose on 3.8 % of the control trials undertaken. For these probes, Category ([1]) was represented twice as often as the ER-protected response Category ([2]]). Accordingly, we tested the ER error protection idea using Chi-square, taking the Category probability imbalance into account when establishing expected frequencies. Chi-square values ranged from 0.53 to 4.08 over Sessions (9 values were <1.0), and only in the latter instance was the critical Chi-square value for 1 degree of freedom exceeded (i.e., 3.84, p < 0.05). These calculations indicate that previous distractor responses were just as likely as Control responses to be used erroneously with target-only probe trials.

Spatial negative priming

Correlated t tests confirmed a visual inspection of the Trial Type (ignored-repetition, Control: spatial negative priming (SNP)) by Sessions interaction in Fig. 3 revealing that SNP differences between Sessions 1 and 3 produced the only significant t values (t[58] = 2.36, p = 022; t[58] = 2.74, p < 0.01, for the target-only and target-plus-distractor probe types, respectively). Discarding Sessions 1 and 2, an original ANOVA pattern using all Sessions changed only in that the significant SNP main effect, F(1, 29) = 179.79, p < 0.01, MSE = 1,531, no longer interacted reliably with Sessions, F < 1. Furthermore, a trend analysis, using within-subject SNP ratio scores (RT [ignored-repetition]/RT [control]), with Probe Type and Sessions (1-14 or 3-14) as main ANOVA factors, revealed a significant linear trend (SNP decline) for the target-only probe trials for both Session numbers; F(13, 406) = 21.06, p < 0.01, MSE = 0.003 and F(12, 348) = 8.04, p < 0.01, MSE = 0.003, respectively (Fig. 4). This did not hold for the target-plus-distractor probes; F(13, 406) = 3.23, p = 0.073, MSE = 0.003 (Sessions 1-14) or F < 1 (Sessions 3-14).

Fig. 3
figure 3

Mean probe-trial reaction times as a function of Trial Type (ignored-repetition vs. control), Probe Type (target-only, target-plus-distractor) and Sessions (224 prime-probe trial pairs/Session).

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Fig. 4
figure 4

Spatial negative priming (SNP ratio, RT [ignored-repetition]/RT [control]) as a function of Sessions (224 prime-probe trial pairs/Session) and Probe type (target-plus-distractor, target-only).

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Collectively, the SNP results revealed that after an initial numerical reduction in size, significant only for SNP difference scores (Fig. 3; Session 1 vs. Session 3); SNP magnitude, however calculated, remained significant and exhibited no further reliable decline over the remaining 12 Sessions, despite a trend in this direction when the probe target appeared alone.

General discussion

Incorrect button-press responses committed on probe trials, where the target appears at a new location (i.e., control trial), are significantly less likely to involve responses associated with prime distractor-occupied locations than to involve responses that were not related to any prime-occupied location (control responses) [Fig. 1; (2) vs. (1), (4) vs. (3)]. These results are consistent with “error protection,” a beneficial inhibitory after-effect that results from the inhibition of the prime distractor response, which then becomes execution resistant (ER). This feature guards against (repels) its wrongful selection on control trials. Notably, this protection extends to responses activated on the probe trial (distractor-repeat trials). The significant bias against choosing former distractor responses on free choice trials, all the more remarkable since the selected-against response is a permissible one, supports the ER repulsion idea (Buckolz et al., 2014; Fitzgeorge et al., 2011).

Unexpectedly, responses related to distractor-occupied probe-trial locations were actually used significantly less often in error than were probe responses tied to an unfilled location (i.e., [1] & [2] > [3] & [4], Scheme 1). Seemingly, the response inhibition mechanism routinely invoked to prevent unwanted response execution of outputs activated by external events is very effective (i.e., automatic self-inhibition, Schlaghecken, Rowley, Sembi, Simmons, & Whitcomb, 2007).

Two further error protection observations are worthwhile. One is that response selection error protection is not evident on target-only, control probe trials (Fig. 2). Importantly, this result confirms the assumption that such control trials do not invoke the prerequisites for the retrieval of stored prime-trial distractor representations; namely, matching prime-probe distractor identities (Fitzgeorge & Buckolz, 2008; Haworth et al., 2014) and/or the activation of the former prime distractor-associated response by the probe target (Buckolz et al., 2012b).

Second, another inhibitory after-effect phenomenon - the inhibition of return [IOR] phenomenon; Posner & Cohen, 1984)—with causes distinct from those of the SNP phenomenon (Buckolz et al., 2012a)—also is held to produce a beneficial inhibitory after-effect. Simply put, the IOR effect reflects the impact of “orientation inhibition,” which is associated with a recently visited location in the visual periphery (Rafal, Calabresi, Brennan, & Sciolto, 1989; Klein, Christie, & Morris, 2005). Relevant here, when individuals search through a static visual display for a designated target (Klein, 2000), orientation inhibition enhances visual search efficiency by discouraging a return or a reorientation to already visited (distractor) locations (e.g., fewer saccade returns to formerly fixated locations: Hooge & Frens, 2000; Klein, 2000). So, the beneficial inhibitory after-effects produced in IOR and SNP tasks both reduce “selection error”; one benefit relates to location selection, the other to response selection, respectively.

While a single inhibitory after-effect espisode is short lived (<10 sec; Buckolz et al., 2008), its underlying processing is persistent. Error protection was remarkably stable over extensive practice using the same task variables, showing it to be a reliable benefit (Figs. 1 and 2). Fundamentally, this stability also held for execution resistance (ER) override time (SNP), although, in contrast to error protection, ER override time showed sporadic reductions over practice (e.g., Session 1 vs. Session 3, Fig. 3; SNP ratio score trend for target-only probes, Fig. 4). These, albeit small differences in practice effects indicate that distractor response inhibition after-effects can exhibit fluctuation independence. Also of note, while escaping ER override time delays altogether is achievable (Buckolz et al., 2012b; Fitzgeorge & Buckolz, 2008; Haworth et al., 2014), it seems difficult to accomplish through extensive practice.

Finally, major SNP accounts do not explicitly comment on inhibitory after-effect longevity or upon its beneficial outcome (Fox, 1995; Houghton & Tipper, 1994; May, Kane, & Hasher, 1995; Neill, 2007; Schlaghecken et al., 2007; Tipper, 2001). The current results provide some guidance on these matters for future SNP theorizing.