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In a novel integration of research designs, we tested for unconscious perception effects at an unattended stimulus location using a focused attention paradigm (Lachter, J., Forster, K. I., & Ruthru...

Two forms of the Stroop task have produced contradictory findings regarding unconscious perceptual processing. Emotional Stroop task studies with prime words presented at an objective threshold (i.e., subliminal) produce Stroop-like effects, but comparable studies conducted with classic Stroop stimuli do not produce Stroop effects. We tested the possibility that differences in the display appearance might explain this discrepancy. Color word prime stimuli from the traditional Stroop task were used with display characteristics based upon the emotional Stroop studies. There was a Stroop effect for the relatively long prime stimulus durations (59, 87, or 108 milliseconds) but not for the brief durations (18, 24, or 38 milliseconds). Accordingly, the discrepancy in research findings cannot be attributed to simple differences in display methodology. The failure to find strong evidence of unconscious perceptual processing is consistent with the negative findings from some emotional Stroop studies that use subliminal stimulus presentations.

A common strategy in unconscious perception research is to use either pattern masking or metacontrast masking to render prime stimuli “invisible” to consciousness. However, several recent studies have questioned whether the identities of prime stimuli (typically arrows or diamonds and squares) in metacontrast masking studies are impossible to consciously perceive. In a series of studies, we concurrently related prime awareness, target response time priming, and prime identification across 3 prime–mask stimulus onset asynchronies (27, 40, and 67 ms). We found that increases in prime awareness ratings were accompanied by better prime identification performance. Significant prime identification in the 27-ms condition was obtained only at the highest awareness rating; for the other 2 stimulus onset asynchronies most awareness ratings were associated with above-chance prime identification. The priming effects obtained in these paradigms occur, to some degree, when participants are likely to be aware of the prime stimuli. Our results, collectively, suggest that metacontrast masking of primes does not necessarily preclude their awareness. Priming effects may depend on at least partial awareness of the prime stimuli.

The Objective Threshold/Strategic Model (OT/S) proposes that strong, qualitative inferences of unconscious perception can be made if the relationship between perceptual sensitivity (typically priming effects) and stimulus visibility is nonlinear and nonmonotonic. The model proposes a nadir in priming effects at the objective identification threshold (identification d'=0). These predictions were tested with masked semantic priming and repetition priming of a lexical decision task. The visibility of the prime stimuli was systematically varied above and below the objective identification threshold. The obtained relationship between prime visibility and priming facilitation was nonlinear, but the results failed to confirm a nadir in priming effects at the objective identification threshold. We conclude that the objective identification threshold does not necessarily indicate the point where presumably unconscious priming effects might be inhibited by conscious cognitive processes.

A key problem in unconscious perception research is ruling out the possibility that weak conscious awareness of stimuli might explain the results. In the present study, signal detection theory was compared with the objective threshold/strategic model as explanations of results for detection and identification sensitivity in a commonly used unconscious perception task. In the task, 64 undergraduate participants detected and identified one of four briefly displayed, visually masked letters. Identification was significantly above baseline (i.e., proportion correct > .25) at the highest detection confidence rating. This result is most consistent with signal detection theory's continuum of sensory states and serves as a possible index of conscious perception. However, there was limited support for the other model in the form of a predicted “looker's inhibition” effect, which produced identification performance that was significantly below baseline. One additional result, an interaction between the target stimulus and type of mask, raised concerns for the generality of unconscious perception effects.

Most studies of unconscious perception aim to demonstrate that the participants are unaware of the prime stimuli (e.g., a measurement of zero sensitivity on prime detection, discrimination, or identification) yet show evidence of perception on another variable (e.g., semantic priming). Dissociation studies of this kind are popular, but the approach has an inherently weak logic. The problem is the need to establish that the awareness measure is exhaustively sensitive to conscious perception (Reingold and Merikle, 1988). The exhaustiveness issue is critical. If exhaustiveness cannot be demonstrated, any findings suggesting unconscious perception can be plausibly attributed to a Type II statistical error (a failure to measure a real effect on the awareness measure) and are open to alternative interpretations. Sandberg et al. (2014) investigated this exhaustiveness issue by comparing two different methods of measuring awareness in an unconscious perception paradigm. The Perceptual Awareness Scale (PAS) is a direct report of stimulus awareness that is expressed on a four point scale (1: no experience, 2: weak glimpse, 3: an almost clear experience, and 4: A clear experience; Ramsoy and Overgaard, 2004). The PAS was compared to an exclusion task that required the participants to intentionally respond in ways that did not match the presented prime stimuli (Debner and Jacoby, 1994; Merikle et al., 1995). Exclusion task results are interpreted as evidence for unconscious perception if the participants match the prime and response at elevated rates (i.e., exclusion failure; an inability to follow instructions presumably due to unconscious perception). Sandberg et al. found significantly elevated prime—response exclusion matches on trials that were rated 1 (“no experience”) or 2 (“weak glimpse”) on the PAS. Exclusion failure at the 2 rating suggested that exclusion failure should not always be interpreted as evidence of unconscious perception because exclusion failure can occur when there is a weak degree of stimulus awareness. The investigators concluded that the PAS is more sensitive (exhaustive) to the presence of conscious perception than the exclusion task. If this is true, then the conclusions of previous studies (e.g., Debner and Jacoby, 1994; Merikle et al., 1995; Smith and Bulman-Fleming, 2004; Matsumoto et al., 2005; Lamy et al., 2008) that interpreted exclusion failure as evidence of unconscious perception may be in doubt because the findings may be partly attributable to conscious perception. Another important implication is that direct measures of awareness (PAS) may be more sensitive than indirect measures (exclusion), which is contrary to the views of some investigators. We would like to support Sandberg et al.'s conclusions by adding that we have obtained similar findings in an experiment that compared an exclusion task to word discrimination performance (Fisk and Haase, 2007; Experiment 3). The participants observed masked word or nonword stimuli that were presented for 75 ms. Half of the trials contained words; the other half, nonwords. Prime sensitivity was determined after each presentation by asking the participants to indicate the presence of a word on a word-nonword discrimination scale that ranged from 1 (“No word was presented”) to 6 (“Yes, a word was presented”). The second response on each trial was an exclusion task. The results from the word trials showed that exclusion failure did not occur at the low discrimination ratings. In contrast, the exclusion failure rate was above baseline and consistent for trials with ratings three through six. This latter result is similar to Sandberg et al. in that exclusion failure was accompanied by evidence that the prime stimuli were consciously perceived. The word/nonword discrimination sensitivity this experiment was da = 0.74, which is well above the zero sensitivity expected for null awareness. When exclusion failure and word-nonword discrimination sensitivity were compared in separate blocks of trials exclusion failure also occurred at display settings with significant prime discrimination sensitivity (58 ms; da = 0.35; 75 ms; da = 0.82; Experiment 2). Overall, these results are consistent with Sandberg et al. in showing that a direct measure of stimulus perception is more sensitive to the influence of conscious perception than the exclusion task. Although these studies reached similar conclusions, there were some noteworthy differences in the results. In particular, Sandberg et al. found exclusion failure effects at the lowest level of the PAS (1—“no experience”), but our study (2007, Experiment 3) found no evidence of exclusion failure at the lower levels of the discrimination rating scale (“1” and “2” ratings; “See Figure 3B of Fisk and Haase, 2007”). Methodology differences may partly explain the discrepancies. The key difference is in the task requirements: the PAS emphasizes reporting stimulus awareness or experience, whereas our word discrimination task emphasized confidence that a word was displayed (i.e., distinguishing words from nonwords). There were other methodology differences too, such as the stimulus displays (0–200 ms vs. 75 ms), stimuli presented on the trials (all words vs. 50% words and 50% nonwords) and setting baseline responses (0 ms vs. nonword trials). Aside from the above differences it is not entirely clear why Sandberg et al. found exclusion success (nonmatching, proper performance) at higher ratings of the PAS whereas our results were essentially the opposite (i.e., exclusion failure—matching—at the higher ratings of word discrimination confidence). We, too, have found exclusion success at high ratings in a 2AFC exclusion task (Haase and Fisk, 2001; Fisk and Haase, 2006). Although there are clear differences between these studies, we would like to emphasize again that the general approach and the main conclusions of both studies—that exclusion failure is sometimes accompanied by significant conscious perception of the target stimuli—are essentially the same. Sandberg et al.'s research provides converging evidence that is an important contribution to our understanding of the influence of conscious awareness in the exclusion task paradigm. Early advocates of using the exclusion task and the Process Dissociation Procedure for studying unconscious perception argued that this approach was advantageous because it circumvented the need to establish null awareness and exhaustive sensitivity (Jacoby and Kelley, 1992; Merikle and Joordens, 1997). In contrast, accumulating evidence from Sandberg et al. and others (Snodgrass, 2002; Fisk and Haase, 2006, 2007, 2013; Bengson and Hutchison, 2007) increasingly suggests that exclusion tasks lack validity for studying unconscious perception. Exclusion failure effects may represent weak conscious perception rather than unconscious perception. Therefore, we feel that investigations of unconscious perception would be better served by using direct ratings of stimulus awareness such as the PAS or other traditional measures, such as detection, identification, and discrimination.

Most investigations of unconscious perception use a dissociation design in which an awareness’variable (e.g., detection) is compared with a perceptual processing variable (e.g., identification). Unconscious perception is inferred when the awareness variable lacks sensitivity to the stimulus but evidence of perceptual processing is still obtained. In two studies we examined the relationship between word identification and detection (Study 1) or discrimination (words vs. nonwords; Study 2) witlh a variety of techniques. In both studies, dissociations suggestive of unconscious perception occurred when the data were examined with subjective threshold approaches, but these differences disappeared when the variables were compared with techniques derived from signal detection theory (SDT). These results do not support unconscious perception in subjective threshold paradigms. In addition, detection appears to be the most sensitive and appropriate task for assessing stimulus awareness, provided that several SDT assumptions are met.

In this commentary, we discuss the strengths and limitations of Snodgrass, Bernat, and Shevrin’s (2004) theory of unconscious perception. Our commentary centers on the value of signal detection theory (SDT) to understanding the unconscious perception controversy, a value that Snodgrass et al. for the most part agree with (i.e., that most approaches to studying unconscious perception are invalid because they have confounded the criterion for detection with the criterion for awareness). However, we believe that their model relies on a somewhat restricted application of SDT. We discuss how SDT can be better applied to provide the necessary tests to validate their model.

BACKGROUND: Traumatic brain injury (TBI) survivors often have sensory and cognitive impairments that may interfere with driving ability. The Useful Field of View (UFOV) is a measure of visual information processing that is a good predictor of vehicle crash risk in older adults. OBJECTIVE: The objective of this study was to explore the possibility that UFOV is compromised after TBI. DESIGN: UFOV performance of 23 TBI survivors and 18 young adults without neurological impairment were compared. CONCLUSION: TBI survivors had higher UFOV scores than young adults, which indicated a greater functional loss of peripheral vision. The results suggest that the UFOV may be a valuable instrument for assessing driving readiness in TBI survivors.

The infralimbic cortex (IL) of the rat can modify autonomic nervous system activity, but the critical pathway(s) that mediate this influence are unclear. To define the potential pathways, the first series of experiments characterizes the descending projections of IL and the neighboring cortical areas using Phaseolus vulgaris leucoagglutinin (PHA-L). IL has prominent projections to the central nucleus of the amygdala (Ce), the mediodorsal nucleus of the thalamus (MD), the lateral hypothalamic area (LHA), the periaqueductal gray (PAG), the parabrachial nucleus (Pb), and the nucleus of the solitary tract (NTS). The density and selectivity of these projections suggest that the LHA and the PAG mediate the ability of the IL to regulate cardiovascular function. The second series of experiments demonstrates that locally anesthetizing neurons in either the LHA or PAG with lidocaine attenuates the hypotensive effects produced by electrical stimulation of the IL. Similarly, microinjections of cobalt chloride (a neurotransmission blocker) into the anterior portion of the LHA also decrease the arterial pressure responses to IL stimulation, suggesting that the ability of lidocaine to reversibly block the evoked response is due to inactivation of neurons in the LHA. These data indicate that hypotension evoked by stimulation of IL is mediated, at least in part, by direct or indirect projections to the LHA and through the PAG.

Past studies indicate that distinct areas of anterior midline cortex in the rat contribute to diverse functions, such as autonomic nervous system regulation and learning, but the anatomical substrate for these functions has not been fully elucidated. The present study characterizes the associational connections within the midline cortex of the rat by using the anterograde transport of Phaseolus vulgaris leucoagglutinin and Fluororuby. The prelimbic area and the rostral part of the anterior cingulate area (both dorsal and ventral subdivisions) are extensively interconnected with each other. In addition, the caudal half of anterior cingulate cortex has extensive projections to precentral medial cortex and caudally directed projections to retrosplenial cortex. Other cortical areas within anterior midline cortex have relatively limited cortical-cortical projections. The infralimbic, dorsal peduncular, and medial precentral cortices have dense intrinsic projections, but have either very limited or no projections to other areas in the anterior midline cortex. Although it has been suggested that cortical-cortical projections from anterior cingulate cortex and prelimbic cortex to infralimbic cortex may be important for linking learning processes with an autonomic nervous system response, the paucity of direct projections between these areas calls this hypothesis into question. Conversely, the results suggest that the anterior midline cortex contains two regions that are functionally and connectionally distinct.

Survivors of traumatic brain injury often have long-term sensory, cognitive and motor deficits that may impair vehicle operation. However, relatively little is known about the driving status and driving characteristics of brain injury survivors. To better understand driving following traumatic brain injury, a survey of driving status, driving exposure, advice received about driving and evaluations of driving competency was administered to a convenience sample of traumatic brain injury survivors (n = 83). The majority of survey participants had experienced either moderate or severe traumatic brain injuries based on the Glasgow Coma Scale. A total of 60% of the survey participants reported that they were currently active drivers. Most individuals (> 60%) who had returned to driving reported driving every day and more than 50 miles per week. Traumatic brain injury survivors frequently received advice about driving from family members, physicians or non-physician health care professionals, but over half (63%) had not been professionally evaluated for driving competency. The presence of high driving exposure, coupled with a lack of widespread driving fitness testing, suggests that some traumatic brain injury survivors have characteristics that may evaluate their risk for vehicle crashes. However, subsequent prospective studies that directly assess driver safety will be needed to confirm this possibility.

Persaud and McLeod (2008) report that unconscious perception is easier to measure with forced-choice exclusion tasks when the stimuli are highly similar, such as choosing between the letters ‘h’ and ‘b’. The high degree of stimulus similarity may decrease conscious awareness of the target stimuli while leaving unconscious cognition intact. The present experiments used forced-choice exclusion tasks (i.e., choosing the opposite of a masked target stimulus) with the aim of replicating these findings. No evidence of relevant perception – either conscious or unconscious – was obtained with short duration targets. The forced-choice exclusion task was correctly performed at longer target durations (25 ms and higher), which suggests conscious perception of the target stimuli. We conclude that increasing stimulus similarity does not reliably produce exclusion failure effects and does not appear to facilitate the measurement of unconscious cognition.

In very old, normotensive rats, a disorganization occurs selectively in the retrosplenial cortex, and a similar disorganization occurs in this area in spontaneously hypertensive rats (SHR) at a much earlier age. Since this breakdown compromises a neural circuit involved in learning and memory, this study tests the hypotheses that these functions are disturbed in mature SHR and that they can be prevented or attenuated by long-term, anti-hypertensive therapy. SHR and Sprague Dawley rats (SD) at 3- and 12 months of age, and a group of SHR that had been normotensive from 3 to 12 months of age (CAP-SHR) were trained on an 8 arm radial maze task. Of the 12-month-old groups, SD reached criterion earliest (28 ± 2 days and made the least number of total errors. In comparison, 12-month-old SHR took significantly longer to reach criterion (39 ± 2 days) and made nearly twice as many total errors. CAP-SHR were intermediate between the other two groups (32 ± 2 days). Three-month-old SD learned the task at the same rate as the 12-month-old SD. In contrast, 3-month-old SHR learned the task significantly faster (21 ± 1 days) and with fewer errors than any other group. These data indicate that, in SHR, learning and memory are compromised by 12 months of age, and that anti-hypertensive therapy with captopril partially prevents this decline.

Elevations in exclusion error rates (i.e., responding with the target stimulus despite instructions to the contrary) in experiments with masked, briefly presented stimuli have been attributed to unconscious perception. The present studies tested the validity of exclusion methods for studying unconscious perception. Experiment 1 replicated Merikle, Joordens, and Stolz (1995; Experiment 1) by showing more exclusion errors (exclusion failure) for masked word stimuli in a stem completion task. However, this experiment did not replicate the finding of fewer exclusion errors (exclusion success) at long stimulus durations. Experiments 2 and 3 showed that exclusion errors are accompanied by significant discrimination sensitivity to the target stimulus, which suggests conscious perception of the target stimulus. Experiments 3 and 4 demonstrated that the exclusion errors obtained from stem completion tasks depend in part on the exclusion method. Altogether, elevated exclusion failure does not provide an unambiguous demonstration of unconscious perception.

Useful field of view is a measure of information processing in peripheral vision that has potential for predicting impaired driving performance. The present study was performed to examine whether common neuropsychological deficits resulting from stroke might be associated with useful field of view impairment. 46 stroke survivors had impaired useful field of view test performance when compared to individuals without stroke ( t30.6= −4.33, p < .001). The impairments in useful field of view of stroke survivors were associated with impaired peripheral fields, slowed processing speeds, and diminished attention. Such impairment was not localized to lesions in any particular brain area. Results allow the inference that common neuropsychological impairments may have contributed to inefficient extraction of visual information from peripheral vision.

Systematic failure to perform exclusion (making a response that opposes the participant’s natural inclinations) for briefly displayed, masked words has been interpreted as evidence of unconscious perception. The present study required participants to make a forced-choice exclusion after viewing masked word targets. The forced-choice exclusion task was properly performed in all experiments, in contrast to previous studies that have utilized stem-completion as a dependent variable. The exclusion failure effects interpreted as unconscious perception in earlier studies appear to be caused by an insensitive dependent variable (stem-completion) rather than unconscious perception.

Objective: Little is known about the extent to which stroke survivors return to driving and the advice and/or evaluations they receive about driving. This study sought to estimate the prevalence of driving after stroke and to determine whether stroke survivors receive advice and evaluation about driving. Design: A convenience sample of stroke survivors was surveyed regarding driving status following stroke, driving exposure, advice received about driving, and evaluation of driving performance. Participants: Two hundred ninety stroke survivors who were between 3 months to 6 years poststroke. Results: Thirty percent of stroke survivors who drove before the stroke resumed driving after the stroke. Stroke survivors are often poorly informed by health care professionals about driving, with 48% reporting that they did not receive advice about driving and 87% reporting that they did not receive any type of driving evaluation. Almost one third of poststroke drivers had high exposure, driving 6 to 7 days per week and/or 100 to 200 miles per week. Conclusions: These findings suggest that many stroke survivors are making decisions about their driving capabilities without professional advice and/or evaluation. The results also suggest that rehabilitation professionals need to devote more attention and resources to driving issues when working with stroke survivors and their families.

Electrical stimulation of area infraradiata in the rat evokes transient changes in arterial pressure, but the locations that evoke these responses have not been mapped by neurochemical methods. To localize more specifically the regions of area infraradiata that modify cardiovascular activity, the present study measured cardiovascular responses to localized chemical stimulation of neurons in area infraradiata of urethane-anesthetized rats ( n =21). Microinjections (50–200 nl) of the glutamate agonist d , l -homocysteic acid into area infraradiata evoked both increases and decreases in arterial pressure and heart rate. Injections in the ventral subdivisions of rostral area infraradiata (IRaα and IRbα) produced cardiovascular responses with the highest probability and greatest magnitude. Of 53 injections in this area, 18 decreased arterial pressure and heart rate, whereas 4 increased arterial pressure and heart rate. In contrast to the results from the ventral subdivision of rostral infraradiata cortex, injections of d , l -homocysteic acid in the dorsal subdivision of rostral infraradiata cortex (IRcα) or any of the caudal subdivisions of area infraradiata (IRβ) produced less consistent changes in arterial pressure. To demonstrate that the general anesthesia did not significantly alter the evoked responses in this study, similar injections of d , l -homocysteic acid were made into area infraradiata of unrestrained, conscious rats ( n =10) and the responses were similar to the responses evoked in urethane-anesthetized rats. These results indicate that the ventral subdivisions of rostral area infraradiata (IRaα and IRbα) are more involved in cardiovascular regulation than other areas of infraradiata cortex (IRcα and IRβ), and that both pressor and depressor sites are present in both areas. © 1997 Elsevier Science B.V. All rights reserved.

The present experiments extend the scope of the independent observation model based on signal detection theory (Macmillan & Creelman, 1991) to complex (word) stimulus sets. In the first experiment, the model predicts the relationship between uncertain detection and subsequent correct identification, thereby providing an alternative interpretation to a phenomenon often described as unconscious perception. Our second experiment used an exclusion task (Jacoby, Toth, & Yonelinas, 1993), which, according to theories of unconscious perception, should show qualitative differences in performance based on stimulus detection accuracy and provide a relative measure of conscious versus unconscious influences (Merikle, Joordens, & Stoltz, 1995). Exclusion performance was also explained by the model, suggesting that undetected words did not unconsciously influence identification responses.