Introduction

Which Value of Consciousness Provides the Foundation for Moral Status?

Human brain organoids (HBOs) are three-dimensional structures artificially induced and grown from stem cells; notably, they have already played an important role as a novel model organism for biomedical research. HBOs are becoming more sophisticated as their structures and functions have become increasingly complex. Over recent years, the possibility that future HBOs may develop further and acquire phenomenal consciousness has been rapidly gaining recognition (e.g. Koplin & Savulescu, 2019; Lavazza, 2020; Niikawa et al., 2022; Sawai et al., 2019, 2022; Shepherd, 2018a). There is consensus that none of current forms of HBOs has consciousness; some also argue that disembodied HBOs cannot be conscious (Croxford & Bayne, 2024). Nevertheless, the possibility of conscious HBOs is not eliminated because HBOs may be embodied in the future, being functionally assembled with sensory and motor systems—which may be biological or nonbiological—in a highly integrated manner (c.f. Kagan et al., 2022). Such a possibility raises several ethical questions, one of which relates to the moral status of HBOs: does their consciousness provide an ethical reason for giving some care to them or refraining from creating them?

Arguably, we should consider the possibility that HBOs acquire negative experiences such as pain. However, it is unclear whether such a line of reasoning should exhaust the ethical issue concerning conscious HBOs. If the possibility of negative experiences is the ultimate rationale, why not eliminate those experiences from the HBO by local anesthesia and leave other experiences—such as visual experiences—open? Using conscious HBOs for experimental purposes, while relieving them from pain experience, would be a case of treating a conscious entity as a means to an end. This, of course, does not violate the Kantian principle that a person should not be treated merely as means; however, conscious HBOs seem to be different from mere “things.”

To clarify why phenomenal consciousness matters, several studies have focused on the notion of moral status. Lavazza (2020) for example, proposes that consciousness in HBOs can be the foundation of their moral status. However, the link between consciousness and moral status is still supposed to be mediated by “subjective interests” (p. 117) associated with negative experiences such as pain. Numerous studies have presented similar arguements(e.g. Chen et al., 2019; Sawai et al., 2019; Shepherd, 2018a) and these views have occasionally been framed within consequentialist perspectives (Koplin & Savulescu, 2019; Lavazza & Massimini, 2018). On the other hand, we could attempt to make sense of the connection between consciousness and moral status more straightforwardly; one might claim that conscious HBOs have a moral status because consciousness has some value in and of itself.

These two possibilities seem to ultimately come down to the question of whether phenomenal consciousness has intrinsic value. Specifically, Sawai et al. (2022) state:

Some draw a distinction between conscious experiences that have a valence (that are good or bad for the subject) and those that do not […]. One moral view is that only experiences with valence have moral value, and thus undergird moral status. Another moral view is that any conscious experience has moral value, and so undergirds moral status. This distinction is relevant to organoids, where one can imagine an organoid with a well-developed visual cortex (say) but no pain system. (Sawai et al., 2022, p. 85; italics original)Footnote 1

These two views are the Neutral View and the Positive View on the value of phenomenal consciousness (Lee, 2019). According to the former, consciousness has no intrinsic value; it has value when conscious mental states involve positive or negative valence, such as a pain experience which inevitably involves negative valence. According to the latter, consciousness has an intrinsic value that does not depend on the valence of the relevant mental state. As Sawai et al. (2022) suggest, according to the Neutral View, conscious HBOs have a moral status when the possibility of pain exists. In contrast, according to the Positive View, a conscious HBO has moral status merely by virtue of its consciousness.

If these views on the value of phenomenal consciousness are thus presented as a rationale in the consideration of the moral status of conscious HBOs, which of these views would be plausible—and how can we justify those views? Interestingly, the justifications used to argue for or against those views are intuitive judgments. Notably, Siewert (1998) urges us to compare living as a normal human being with living as a functional duplicate devoid of consciousness—a “zombie”—and argues that you would judge the human life to be clearly preferable and, therefore, the Positive View is plausible. However, this thought experiment is too crude to draw implications about the value of consciousness because we, unlike zombies, experience various mental states involving positive valence. Imagining the psychological life of a zombie, which is devoid of such experiences, may prompt us to conclude that our human existence is preferable to the zombie life. In this case, the Neutral View would be compatible with the intuitive judgments.

In this regard, Lee (2019),who supports the Neutral View, draws on a more subtle thought experiment. He urges us to compare a world in which there is an organism that is only minimally conscious and lacks any valence-involving experiences—for example, an organism with only a visual experience of light—with a world in which the organism is nonconscious throughout its life, for example, because it is sleeping. He argues:

If you think that the consciousness world is better than the non-consciousness world even after taking these methodological precautions, then you favor the positive view. On the other hand, if you think that there is nothing better about the world where the creature is conscious, then you favor the neutral view. Speaking for myself, [...] I find it hard to see why we should think the world with consciousness is better than the world without. (Lee, 2019, p. 664)

Notice that the organism imagined herein is little different from HBOs with only visual experiences in important respects. Thus, intuition about the HBO-like organisms that only have visual experience is invoked to support the Neutral/Positive Views. However, as Sawai et al. (2022) state, the Neutral/Positive Views are invoked to consider the moral status of conscious HBOs, especially HBOs with only visual experiences. Thus, if we collect the pieces of existing inferences within the literature, reasoning appears in a circular manner: (1) in order to determine the moral status of conscious HBOs without pain, we need a theory about the value of consciousness; (2) under such a theory, the value of consciousness must be either valence-dependent or valence-independent, where the Neutral and Positive Views compete with each other; (3) however, the basis for assessing the Neutral and Positive Views is the status of the hypothetical organisms that is little different from HBOs without pain, that is, those with only a visual experience of light. Perhaps this circularity can be avoided by appealing to the intuition about the hypothetical organism, as Lee does. However, while Lee’s intuition about the organism is supposed to support the Neutral View, there is no guarantee that the same intuition can be reproduced beyond their judgment. Although Lee would claim that it is never intuitive that an HBO-like organism with only a visual experience has any value, their intuition might be an idiosyncratic one. There may be rather, as a psychological fact, a general tendency for intuition to work the other way round.

Introducing the Approach of Experimental Ethics

To make progress, we think it is helpful to empirically examine how people’s intuitions work. An empirical examination would provide a foundation to determine whether the value that people have in mind can be consistent with certain theoretical views. Such a form of empirical examination has been recently utilized to address various issues in bioethics and neuroethics, drawing on the methodology of experimental ethics (Earp et al., 2021; Lewis et al., 2023; Reiner, 2019). In our estimation, this methodology has the potential to indicate which view on the value of consciousness is justified, at least prima facie. Indeed, as can be discerned from the quotation above, Lee’s thought experiment is offered with the implicit methodological commitment such that the justification of the view on the value of phenomenal consciousness depends on how our intuitions work. The general idea behind this commitment will be that any arguments concerning ethical inquiries need to hinge on premises found to be intuitively true. Therefore, we can—and perhaps we should—rely on an empirical examination with a sample size large enough to allow for a statistical elucidation of the general trends regarding intuition.Footnote 2 We focus on the general trends because intuitions obtained from a small number of people—such as Lee’s intuition stated in the above quotation—may be idiosyncratic ones.Footnote 3 Of course, there is a possibility that no straightforward trends exist in intuition; however, that is also a matter to be determined empirically.Footnote 4

In adopting the empirical approach, first, we think it is better to examine the intuitive judgments about hypothetical conscious HBOs, not the imaginary conscious organisms in Lee’s case. This is because abstractly constructed thought experiments, such as Lee’s, may be filled with different details assumed in different subjects; such details should be aligned for the purpose of “cleanly isolating the relevant intuitions” (Lee, 2019, p. 662). Second, to determine the nature of intuition, empirical investigations with systematic manipulations would be insightful. Existing psychological research has often shown that we are inefficient at determining what factors influence our own judgment and decision-making (Hauser et al., 2007; Johansson et al., 2005; Nisbett & Wilson, 1977). By presenting people with hypothetical vignettes about HBOs and manipulating the descriptions related to consciousness, we can explicate whether the intuition is sensitive to a specific type of consciousness (e.g., only to the presence/absence of pain experience) or to any type of consciousness (e.g., whether they are also sensitive to the presence/absence of visual experienceFootnote 5).

We acknowledge that the empirical examination could be a qualitative style. Indeed, several qualitative studies have examined patients’ and people’s attitudes toward HBOs based on the interview methodology (Boers et al., 2018; Bollinger et al., 2021; Haselager et al., 2020; c.f. Ravn et al., 2023).Specifically, they have observed that brain organoids evoke various ethical concerns unlike other types of organoids; generally, some of those concerns seem to be related to the idea the brain plays a crucial role in the human mind (Bollinger et al., 2021). Furthermore, it has been observed that such concerns arise from thoughts about the possibility of HBOs being conscious (Haselager et al., 2020; Ravn et al., 2023). However, the quantitative approach would be advantageous to examine whether such ethical concerns are generally shared among people or not; moreover, it would enable us to determine what factors drive such ethical concerns and how those factors interact. Relatedly, in those existing studies, it is unclear whether the participants were aware of important distinctions, such as the one between phenomenal consciousness and self-consciousness or the distinction between phenomenal consciousness that does or does not involve valence. This lack of clarity can be overcome by systematically manipulating the information presented to people and quantitatively analyzing their responses.

Therefore, we conducted a quantitative, experimental ethics study to investigate how people potentially evaluate the value of consciousness that can ground the moral status of HBOs. In doing so, we presented the participants with hypothetical descriptions about HBOs and collected their responses, manipulating the presence/absence of pain and visual experiences in the vignettes. We thereby attempted to elucidate the value that people ascribe to phenomenal consciousness and how it manifests in their intuitive judgments regarding HBOs.

Experiment

Participants

We recruited our participants through Prolific, a crowdsourcing service. A total of 600 individuals participated in the study, of whom 357 were included in the analyses (criteria for data exclusion are described below).Footnote 6 The final sample of 357 participants in the analyses consisted of 144 males and 202 females (11 were either “Non-binary/Other” or preferred not to share their gender), ranging from 20 to 75 years (M = 33.16, SD = 11.84). They mainly resided in the United Kingdom (37%) and the United States (31%), had bachelor’s degrees or higher (60%) and either did not belong to any specific religion (57%) or were Christians (31%). All of them used English as their first language.

This study was approved by the Ethical Committee of Niigata University and was conducted in December 2021.

Procedure

After giving us their informed consent, the participants were presented with a description about HBO research. The description consisted of two parts: the first part was the same for all conditions and provided the participants with a general account of the development of HBO research; the second one differed across conditions and instructed the participants to imagine future HBOs with or without phenomenal consciousness.

The first part was as followsFootnote 7:

In recent years, scientists have been developing a new technology to create ‘brain organoids’. A brain organoid is a collection of nerve cells, which are the building blocks of the brain. Brain organoids are created from cells taken from human embryos or human body parts such as skin. Scientists artificially induce embryo or body-part cells to immature cells called stem cells. The stem cells are then developed into nerve cells.

It is hoped that brain organoids will enable scientists to conduct new experiments that they cannot perform using human brains and will thus lead to advances in neuroscience and medicine.

Fig. 1
figure 1

Distribution of the moral permissibility judgment

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The second part was manipulated with respect to two factors: whether the HBOs have visual experience and whether they have pain experience. This manipulation produced four variants of the description. For exploratory purposes, a fifth variant that made no mention of the HBOs’ sensations was added, although this condition was not included in this study’s analyses. The participants were randomly assigned to one of the five conditions described as follows:

  1. (1)

    Vision−/Pain− condition.

    Now imagine that in the future, further research developments permit the creation of brain organoids that are similar to the human brain in cell shape and function but do not have any sensations such as vision and pain.

  2. (2)

    Vision+/Pain− condition.

    Now imagine that in the future, further research developments permit the creation of brain organoids that have visual sensations. They feel brightness when exposed to light but do not have other sensations such as pain.

  3. (3)

    Vision−/Pain+ condition.

    Now imagine that in the future, further research developments permit the creation of brain organoids that have pain sensations. They feel pain when physically stimulated but do not have other sensations such as vision.

  4. (4)

    Vision+/Pain+ condition.

    Now imagine that in the future, further research developments permit the creation of brain organoids that have visual and pain sensations. They feel brightness when exposed to light and feel pain when physically stimulated.

  5. (5)

    Control condition (not included in the analyses).

    Now imagine that in the future, further research developments permit the creation of brain organoids. They are collections of nerve cells artificially cultivated from human embryo or body-part cells.

The participants were then asked to judge the moral permissibility of the actions toward the HBOs by indicating their agreement with the four statements mentioned below (1: “Strongly Disagree” to 7: “Strongly Agree”). These statements were presented in a random order and the participants were explicitly instructed to respond while keeping in mind the described HBOs.

  1. (a)

    It is morally permissible to create the type of brain organoids described above.

  2. (b)

    It is morally permissible to use the type of brain organoids described above for research purposes.

  3. (c)

    It is morally permissible to expose the type of brain organoids described above to physically damaging stimuli such as electric shock without stipulating a research purpose.

  4. (d)

    It is morally permissible to physically destroy the type of brain organoids described above without stipulating a research purpose.Footnote 8

Next, the participants responded to manipulation check items asking them about the HBOs they assumed when answering the above questions. The items were “It can feel pain” and “It can feel the brightness of a light” (1: “Strongly Disagree” to 7: “Strongly Agree”). The participants whose responses were inconsistent with the description in each condition were excluded from the analyses. Specifically, we excluded those who responded to the former item with a value of 5 or more in Pain− conditions or a value of 3 or less in Pain+ conditions. We also excluded those who responded to the latter item with a value of 5 or more in Vision− conditions or a value of 3 or less in Vision+ conditions. In addition, an attention check item instructed participants to choose “Slightly Agree.” Those who failed to follow this instruction were excluded from the analyses.

Data exclusion

We excluded the participants who were assigned to the fifth condition, which was irrelevant to the analyses in this paper (n = 122), those who failed to correctly respond to the attention check item (n = 6), and those who showed responses inconsistent with the presented description in the manipulation check items (n = 115). Finally, 357 individuals were included in the main analyses.Footnote 9

Results

We analyzed the participants’ judgment about the moral permissibility of the actions toward the HBOs. Figure 1 and Table 1 show the distribution and the mean scores of the responses, respectively.

Table 1 Mean scores of the moral permissibility judgments
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A three-way analysis of variance (ANOVA) was conducted to test whether the moral permissibility judgment was affected by the presence/absence of pain experience, the presence/absence of vision experience (between-participant factors), and the type of action (a within-participant factor), as well as the interactions among them. This revealed that the main effects were all significant [Pain: F(1, 353) = 18.53, p < 0.001, ηp2 = 0.050; Vision: F(1, 353) = 5.14, p = 0.024, ηp2 = 0.014; Act: F(3, 1059) = 184.79, p < 0.001, ηp2 = 0.344], whereas no interaction was detected (see Table 2). Specifically, actions toward the HBOs with pain experiences were judged to be less permissible than those without pain experiences, regardless of the action type. The presence of visual experiences showed a similar effect, although the effect size was smaller than the factor of pain experiences.Footnote 10 The type of action also showed a significant main effect, and the multiple comparisons using Shaffer’s method revealed that using the HBOs was deemed the most permissible, followed by creating the HBOs and destroying them. Exposing them to physically damaging stimuli was the least permissible. The comparisons were significant in all pairs [ts (353) > 2.06, ps < 0.040].

Table 2 Result of the ANOVA regarding the moral permissibility judgments
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Discussion

We conducted an experiment to examine how people judge the permissibility of various actions toward HBOs and how these judgments are sensitive to features related to phenomenal consciousness. To this end, the descriptions of HBOs presented to the participants were manipulated in terms of two factors: whether the HBOs had pain experience and whether they had visual experience. We now discuss the experimental results in terms of the psychology of moral status and its normative implications.

Before doing so, we note the overall trend in the participants’ reactions to the actions toward HBOs. The participants did not show negative attitudes toward creating and using HBOs; their moral permissibility judgments about creating HBOs were between 5.51 through 4.59, which were all above the midpoint; those about using HBOs were between 5.77 through 4.73, also all above the midpoint.Footnote 11 These results are consistent with the existing qualitative studies reporting that patients and the general public are supportive toward HBO research (Boers et al., 2018; Bollinger et al., 2021; Haselager et al., 2020; Ravn et al., 2023). As those studies also  show the concern for the possibility of consciousness emerging in HBOs, we are interested in how the participants’ moral permissibility judgments are affected by manipulating the information about consciousness. Moreover, it will be informative to see how the participants’ moral judgments are sensitive to not only the presence/absence of consciousness but also the difference in the valence of consciousness. This is because, as discussed in Sect. "Introduction", the theoretical considerations have been indecisive between the valence-dependent and -independent values of consciousness in considering the moral status of conscious entities. Keeping these interests in mind, we first discuss what our results suggest for the psychology of the moral status of (non)conscious HBOs.

Psychology of the Moral Status

As revealed by the ANOVA, the permissibility judgments were sensitive to the presence/absence of pain experience in the HBOs. Specifically, actions such as creating HBOs that experience pain tended to be regarded as less permissible compared to HBOs that do not experience pain. This inclination seems to be consistent with both the Neutral and Positive Views. For, on the one hand, it fits with the Neutral View, especially the version in which the moral status of conscious HBOs is solely grounded in the valence of experience. For example, views such as Lavazza (2020), which seeks to ascribe the moral status of conscious HBOs to “subjective interests,” might be successful in capturing this moral sensitivity. On the other hand, this moral sensitivity is also consistent with the Positive View, which holds that consciousness provides the foundation for the moral status, regardless of the valence of the conscious mental states; the importance of pain experience is derived simply from the fact that the relevant mental state is conscious. It is therefore crucial to look at the sensitivity to the presence/absence of visual experience to test whether people’s intuitive judgments best fit with the Neutral or Positive View. The results show that the judgments were sensitive to the presence/absence of visual experience; notably, the actions against the HBOs that experienced vision tended to be regarded as less permissible compared with the ones that did not experience vision. This finding suggests that the value of consciousness that people find in conscious HBOs cannot be fully explained by the valence of the relevant mental states.

The above consideration still leaves two possibilities. The first is that only the valence-independent value of consciousness is endorsed in people’s intuition as the foundation for moral status. The second possibility is that, while the intrinsic value of consciousness is endorsed, the additional significance of the valence of conscious mental states is recognized. While further empirical studies are needed to decide between these possibilities, our results favor the second one. This is because, if the first possibility is true, there should be no discernible difference in the effect of visual and pain experiences on people’s judgments. However, the results suggest the contrary, as the effect size of pain experience (0.050) was greater than that of visual experience (0.014).Footnote 12 If this reasoning is correct, no major existing views on the moral status of conscious HBOs fully capture the moral sensitivity involved in people’s intuition. Perhaps both the valence-independent and the valence-dependent values are found important, each of which is isolated by the Positive View and the Neutral View respectively. This appears to mirror the general trend in experimental philosophy such that each of competing philosophical views finds its corresponding intuition in people’s mind (e.g. Deery et al., 2015; Dranseika, 2024; Isern-Mas & Hannikainen 2024).Footnote 13 Notice that this possibility is different from existing proposals that seem to define the multiple layers of the value sustaining moral status. For example, Koplin and Savulescu (2019) propose different modes of moral consideration for conscious HBOs and those with additional cognitive abilities such as autonomy or self-awareness. In contrast, the moral sensitivity identified in the present study seems to define the layers of value inside phenomenal consciousness. For, in other words, people seem to—at least implicitly—acknowledge both the valence-independent and the valence-dependent values of consciousness.

It is, however, still possible that only the valence-independent value of consciousness is endorsed, given that the relevant effect sizes may not be significantly different. In this case, the situation appears sharper because, to our knowledge, no explicit theoretical views have been developed to claim that only the valence-independent value matters in the moral status of HBOs. In any case, our baseline finding shows that the valence-independent value is endorsed in the moral sensitivity involved in people’s intuitive judgment, whose normative implications we will discuss shortly (see Sect. "Normative Implications for the Moral Status").

Contrary to these explanations, the following possibility may be pointed out: people are committed only to the valence-dependent value, whereas the conscious mental states without valence—such as visual experience—are perceived merely as cues to assume the presence of conscious mental states with valence. Hence, the sensitivity to visual experience does not reflect the nature of people’s moral intuition; instead, it is a sort of performance error. However, we checked whether the participants correctly assumed the presence/absence of visual and pain experiences and excluded from the analysis those participants who provided responses that were inconsistent with the presented descriptions. In particular, only 16 of the 118 participants provided an incorrect response to the statement “it can feel pain” in the Vision+ /Pain− condition, which was fewer compared to the 26 of the 116 participants who responded incorrectly to the statement “it can feel pain” in the Vision−/Pain− condition. Therefore, the possibility of performance error is not supported. We acknowledge that there may be further alternative explanations. For example, visual experience is a cue for self-consciousness, and it is the value of self-consciousness to which people are truly committed. Although we cannot rule out such explanations, we think it would be reasonable to accept the explanation that people are at least partly committed to the intrinsic value of consciousness, in the absence of empirical evidence for alternative explanations.Footnote 14

Normative Implications for the Moral Status

The abovementioned psychological considerations potentially have normative implications for the ethics of HBOs. The most straightforward implication would be that theoretical views consistent with the identified moral sensitivity involved in people’s intuitive judgments are prima facie justified. Indeed, intuition has been given a justificatory role regarding the value of consciousness, as can be discerned in the argument presented by Lee (2019) (see Sect. "Introducing the Approach of Experimental Ethics"). However, our investigation revealed something contrary to what Lee intuited. Lee might expect that the intuition regarding HBOs would be manifested in a manner that aligns with the Neutral View; that is, visual experience does not matter because it does not have a valence-dependent value of phenomenal consciousness. In contrast, our results show that people’s intuition about HBOs works oppositely, as the presence of visual experiences in HBOs prompted people to deem it less permissible to create or destroy the HBOs. Therefore, if there are any ideas that can be prima facie justified by intuition, it should not be that the moral status of conscious HBOs is solely grounded in the valence-dependent value of consciousness.

The following objection could be raised about this line of reasoning for the justification by intuition. Ethical views are justified by their harmony with general principles rather than intuitions about individual cases (Singer, 2005); if they are in opposition, general principles should have greater weight in justification. For example, in the present case, it might be attempted to propose an argument for the general principle that phenomenal consciousness is important because of the valence of conscious mental states, thereby discarding the moral sensitivity that indicates the valence-independent value of consciousness. However, such an objection is less stable than it appears. As we have explained, the general principles that support the significance of consciousness in HBOs are supposed to be Neutral/Positive Views on the value of consciousness, and these views rely considerably on intuitions about individual cases, such as the one presented by Lee (2019). Thus, intuitions about such individual cases cannot be deprived of their justificatory role.

However, the robustness of this justification is another matter, and this is why the justification is prima facie. Even if the justification is conferred in the manner that we have discussed, it may be overturned by other moral reasons. For example, if biomedical research involving visually conscious HBOs could greatly advance the field of medicine and bring enormous benefits to patients, then these benefits may be prioritized instead of the concern for consciousness. After all, biomedical research using various conscious model organisms has been permitted under certain regulations. Nevertheless, the present study prompts us to consider the idea that the moral significance of consciousness is not exhausted by the valence-dependent value of mental states such as pain experiences. Leaving aside the extent to which such an idea carries more weight than other moral reasons, the present study suggests that the presence of consciousness in HBOs—independent of its valence—should be a candidate to weigh against other moral reasons.

Another concern is that moral intuitions can be formed in different ways in different cases; especially, the intuition we have identified in the present study may conflict with intuitions about other cases. Therefore, the justification we have discussed may be overturned by those intuitions. Indeed, we can find many other cases discussed in relation to the value of consciousness in existing literature (Lee, 2019; Siewert, 1998). Some of these endeavors conclude that the value of consciousness has to be valence-dependent in providing the foundation for moral status (Shepherd, 2018b). In reply, we acknowledge that the intuition involving the moral sensitivity identified by the present study can be overturned by some other intuitions. However, it should be shown why such intuitions are to be prioritized than the one focused on in the present study. One possible reason could be that, for example, prioritizing them makes more sense in systematizing all relevant aspects of how our intuitions work. If this is the case, it remains to be empirically observed how intuitions work in broader cases related to the value of consciousness; it should be shown that there is any intuition truly inconsistent with the moral sensitivity identified by the present study. In either situation, one cannot discard the findings in the present study simply by pointing out the possibility of justificatory overturn.

In light of the above discussion, our fingings put pressure on the theoretical view that the moral status of conscious HBOs is solely grounded in the valence-dependent value of consciousness. As we have discussed, our results leave the possibility that both the valence-dependent and the value-independent values are deemed important (See Sect. "Psychology of the Moral Status"). However, given our finding implying that the valence-independent value of consciousness is endorsed in people’s intuitive moral judgments, it deserves serious consideration to construct such a theoretical view that the moral status of conscious HBOs is grounded in the valence-independent value of consciousness. Considering this view, actions such as creating, using, and destroying conscious HBOs are to be differentially evaluated than those actions toward nonconscious HBOs; therein conscious HBOs to be respected include not only those with pain experience but also those with visual experience. Alternatively, we are required to show why such a theoretical view should be dismissed, either by undermining the prima facie justification conferred by the intuition observed in this study or explaining away the present observation with further empirical examination.

The present study has further practical implications beyond those considered so far. As explained in Sect. "Introduction", the future possibility of conscious HBOs highlights the importance of the debate over the value of consciousness, which motivated our present study. However, the present study is still informative for the skeptics about the future possibility of consciousness in HBOs. From the conjunction of skepticism about conscious HBOs and our psychological finding that people’s moral intuition involves the sensitivity to the presence/absence of consciousness, we should be led to the thought that the problem of consciousness in HBOs has to be actively de-emphasized. For, as we have observed, perceiving that HBOs may acquire consciousness—regardless of its valence—negatively affects negatively people’s attitudes toward creating them. Therefore, if it is an in-principle truth that HBOs cannot acquire consciousness, we should count such a tendency of people’s attitudes as a factor premised on a misunderstanding and make an effort to deter this factor.

Relatedly, a recent qualitative study (Lavazza & Chinaia, 2023) reported that experts were generally skeptical about the possibility of consciousness in the current HBOs (see also Lavazza & Chinaia, 2024 for further discussion). However, it is noteworthy that the experts’ stance about the future possibility was not wholly dismissive; and more interestingly, the experts were inclined to accept the conditional idea that HBOs would be handled differently if consciousness is detected in HBOs (Lavazza & Chinaia, 2023).Footnote 15 Given these observations, it may be that the moral sensitivity to the presence/absence of consciousness is not so different between laypeople and experts. Perhaps the future possibility of conscious HBOs can be important to both experts and laypeople as an issue that plays the role of input to moral intuition, whether it is finally affirmed and emphasized on the one hand or denied and de-emphasized on the other hand. In exploring further these implications, it will be helpful to examine people’s and experts’ moral intuitions in a more systematic and comparative manner.

Another implication is about valence. As we have argued, the present study puts pressure on the view that the moral status of HBOs is solely grounded in valence-dependent value. However, suppose that all in all, this view is justified. Even in this case, our psychological finding that the valence-independent value of consciousness appears important for people’s moral intuition would be informative. For, given our finding, we should be cautious about creating and destroying conscious HBOs that are free from valence-involving experiences in the future. Although such actions are morally insignificant (by hypothesis), our findings predict that the public will find such actions morally significant to some extent. This may harm the public’s trust in the sciences of HBOs and could decelerate its development in society (Fitz et al., 2014; Roeser & Pesch, 2016). By providing such predictive analysis, we think that our finding can inform how we could more effectively support HBO research in society.

Concluding Remarks

People’s moral intuition is sensitive not only to the presence/absence of pain experience but also to the presence/absence of visual experience in HBOs. Therefore, at least implicitly, people acknowledge the valence-independent values of consciousness in considering the moral status of conscious HBOs. This finding puts pressure on the theoretical view that the moral status of conscious HBOs is solely grounded in the valence-dependent value of consciousness.

In the remainder of the paper, we undertake two tasks. First, we provide a methodological reflection on the normative reasoning we have engaged in. Second, we discuss a couple of limitations of our study in terms of its empirical validity.

Styles of Normative Reasoning

In this study, we examined how moral intuition works regarding the future possibility of conscious HBOs and discussed its normative implications. As we adopted the methodology of experimental ethics, it is worth to note how our study can be situated within the broader normative character of experimental ethics.Footnote 16 Explicating such normative character, Earp et al. (2021) summarize the four styles of normative reasoning from empirical datum: parsimony, debunking, triangulation and pluralism, which are not mutually exclusive. Our present study seems to follow at least two of these, as we will explain in the following.

First, the most obvious style found in our major line of reasoning is parsimony, according to which people’s moral judgment has prima facie normative weight, in that we attempted to support/reject specific theses about the value of consciousness by appealing to how people’s intuitive judgments work. However, our reasoning was not so simple like “it is justified that p, because people intuitively judge that p”. Rather, we focused on what factors people’s moral intuition is sensitive to. This is no trivial difference, because it is rather usual that people are not aware of the sensitivity involved in their own ideas in contrast to the contents of those ideas (see Sect. "Introducing the Approach of Experimental Ethics"). Second, our normative discussion contains triangulation, which adjusts and combines multiple (sometimes conflicting) views from various stakeholders to create a coherent one. We believe we have exemplified this in our discussion of the balance between the prima facie justified moral status of conscious HBOs and the benefits of biomedical research using them (see Sect. "Normative Implications for the Moral Status").

In contrast, pluralism, in which multiple views have normative weight without assuming their coherence, was not explored in our discussion. However, we could attempt to offer pluralism, for example by incorporating the psychological possibility that both the valence-dependent and valence-independent values of consciousness are endorsed in people’s moral intuition (see Sect. "Psychology of the Moral Status"). In addition, we did not attempt debunking, which is a style of reasoning to unjustify observed intuitive judgments—and a theoretical view associated with them—by finding unreliable psychological backgrounds. This is simply because it goes beyond our motivation of asking which values of consciousness is endorsed in people’s moral intuition. However, alternative explanations to the observed patterns of intuition may be provided, possibly leading to the debunking argument such that the intuition and any related views about the value of consciousness are unjustified. In particular, it is interesting to see whether people distinguish between phenomenal consciousness and self-consciousness; it may be that the intuition favoring the valence-independent value arises from incorrectly assuming self-consciousness when reading the description of visual experience (see Sect. "Psychology of the Moral Status"). Future empirical studies are expected to test these empirical possibilities and thereby contribute to further normative discussions.

Limitations in the Empirical Aspects

There are some limitations in our study, two among which are worth noting.

First, we adopted visual experience and pain experience to represent phenomenal consciousness with and without valence, respectively, to examine the moral intuition. This selection is motivated by the existing studies discussing the value of phenomenal consciousness. However, it is important to explore whether the findings we have observed can be generalized into other various modalities of phenomenal consciousness. For example, as a case of phenomenal consciousness with valence, it could be helpful to test how moral intuitions work about positive experiences such as joy and pleasure. As a case without valence, we could also consider other perceptual/sensory modalities such as auditory or olfactory experiences. It may be that, when confronted with these various types of phenomenal consciousness, moral intuitions work in different manners from what we have observed.Footnote 17 There is a need for more empirical works incorporating these possibilities in order to determine the precise nature of moral intuitions.

Second, our study is limited because all participants were English speakers, mainly from the UK and the US. There is no guarantee that similar results would be obtained across other populations. Indeed, it has been argued that one cannot assume uniform psychological tendencies related to philosophical issues across cultures (Knobe et al., 2012). Moreover, it has been pointed out that psychological research is biased toward particular groups and attributes of people and, accordingly, related empirical findings are not always generalizable (Henrich et al., 2010). Regarding these possibilities, we think it would be interesting to conduct further research that incorporates comparative observations across multiple cultural backgrounds or explores connections to various psychological factors such as individual differences in moral values. Such empirical investigations should explicate the complexity of moral sensitivity involved in people’s intuition and inform the ethical debate over the future possibility of conscious HBOs.