1. Introduction

This is HCI, the acronym for an ever-changing field in a constant effort to arrive at better modalities for people to interact with digital systems. From the early command-line interfaces to the, by comparison, graphically rich interfaces today, the movement has always been to make the interaction increasingly intuitive and productive. Very recent developments in this respect are Tangible User Interfaces (TUI). TUIs contrast with GUIs by incorporating direct and physical interaction, allowing users to work on real-world objects to control and manipulate digital information [1, 2]. Such a trend towards tangibility is directly connected to the way human beings process information in both a cognitive and sensory manner. It, therefore, means that it allows for more natural and multisensory use of technology [3].

From cognitive ergonomics and education to industry, the prospects for TUIs are immense. This improves memory by reducing cognitive load, thus allowing for more effective and interactive communication. Integration of TUIs with advanced possibilities of IoT opens completely new perspectives in the field for smooth and intuitive smart system management [4]. On the contrary, TUI involves very high technological requirements and huge financial investments in development, while users have received this with reserve due to the novelty of interaction methods. The paper reviews applications, especially on the use of TUI in cognitive ergonomics, education, and industry. It provides a bit of historical background on interaction paradigms in HCI-from CLI to GUI and now to TUI-with practical, detailed case studies and theoretical frameworks to support the argument on benefits of tangible interaction in respect of cognition. Besides describing the benefits, it enumerates the challenges regarding scalability and accessibility issues in TUIs, opening up avenues for possible solutions.

An account is created for the integration of TUIs into IoT for the potentiality of revolution in user interaction in smart environments.

2. Explanation of paradigms of interaction in HCI

Early CLI systems, such as Unix, required users to memorize commands to perform tasks. Although it was efficient for technical experts, it was not an easy task for ordinary users. With the emergence of GUIs, such as the Xerox Alto, it made user operations easier through icons and windows. It was much easier to drag and drop files than to enter complex commands. Later, Apple's Macintosh popularized this concept to the public.

TUIs represent a completely new paradigm in integration and embedding physical objects directly into virtual worlds, allowing natural, intuitive, and multisensory interaction. Probably the clearest line of evolution in paradigms of interaction to be seen in HCI so far has been the one from CLIs to GUIs. A classical example of a CLI is the old Unix operating system, whereby even for basic functions like handling files, users had to insert commands by using special textual syntax. This was indeed a powerful and quick way for the power user, but it was a steep learning curve for the beginner as it required much memorization and syntax of commands. The advent of GUI, as done in the Alto computer by Xerox, was a paradigm shift, as now the interface used visual representations of objects like icons and windows, and the mouse directly manipulated virtual entities on the screen [1].

An example would be how Xerox Alto controlled its files by dragging and dropping them into their respective folders, which was way easier than spelling the commands out. Later, Apple Macintosh adopted this and made personal computers even more accessible to mainstream audiences by greatly reducing the mental work one had to engage in to operate a computer. While GUIs for the most part depend on device use, such as the mouse and keyboard, for indirect interaction, hence distancing the user action from digital outcome. TUIs enter in here to bridge that gap. TUIs provide a new paradigm whereby digital functions are embedded in physical things; it allows the user to interact with digital information using real-world objects.

This would immediately connect the physical world with the digital. The emergence of TUIs is a part of a broader HCI movement toward further trends toward more embodied, multimodal, and intuitive interaction that better matches human perception and cognition. Figure 1 shows the Xerox Alto Graphical User Interface.

Figure 1. Xerox Alto graphical user interface [5]

2.1. TUI- A new paradigm of interaction

In many ways, TUIs are rather unlike traditional GUIs; however, they present a different interaction paradigm than the former. While GUIs challenge users mainly as a visual medium, requiring indirect manipulation by device, TUIs let users interact directly with digital information physically by using everyday objects. Here, it shifts away from the abstract visible representations to a more hands-on experience where users can apply their tacit skills in the handling of physical objects to interact with digital information. With tangibility in presentation, spatial interaction, and immediate feedback, TUIs are notable. A rather classic example of TUI is "Reactable," an electronic musical device taking in a tabletop format. By moving and placing physical objects on top of a semi-transparent surface, the user creates and controls audio. Each of these objects symbolizes something-for example, a synthesizer or some effect-in itself a presentation of the concept of tangibility in presentation.

If users move these objects around or change their orientation, the spatial interaction mechanism translates such changes into related changes within the soundscape, hence offering an unusually intuitive control paradigm. Instant audiovisual feedback is afforded because immediacy of response shows up on the table itself, allowing users to perceive instant results of their actions and thus fostering an immersive, non-discrepanant experience. Another example was the "inFORM" project from the MIT Media Lab. That is a dynamic shape display: a screen with a grid of actuators set into pins that express 3D objects which can be manipulated physically. Digital content would come through these pins by direct contact: rising and falling in real time to render shapes and create spatial interaction with a physical, 3D space.

It is providing immediate feedback: the height of the pin changes instantly after a user input, thus materializing the digital information. Such a bridging of the gap between the physical and digital world opens a whole new space for innovative interaction, from collaborative design to the physical visualization of data.

These are the tangible manipulation, spatial interaction, and immediate feedback that provide a more intuitive and natural interaction paradigm than state-of-the-art interfaces [3, 4]. In TUIs, because users interact with digital information by means of physical means, they make use of their cognitive ability to reason in space and to move, hence providing better cognitive ergonomics and a greater feeling of engagement.

2.2. Enhanced cognition in processing with TUI

Another very encouraging reason to consider the alternative interaction paradigm is in relation to cognitive processing of TUI. TUI reduces the distance between action and perception, hence enabling the user to interact with the digital content in a way very proximal to how things really happen. For this reason, direct handling of physical objects cuts down on the cognitive efforts of translating abstract digital commands into meaningful actions, hence enhancing cognitive processing.

The theoretical and empirical evidence in cognitive science, particularly in the theories of distributed cognition and embodied cognition, supports tangible interaction with cognitive benefits [6]. According to the distributed cognition theory, the process of cognition does not subsist in individual minds but rather is dispersed among objects, individuals, artifacts, and tools in the environment. This provides an excellent basis for TUIs to externalize the cognitive tasks as physical manipulations so that mental workload decreases.

One such is the UR-P system of urban planning developed at the MIT Media Lab, which, even though based on a digital mapping platform, has been given the twist of being able to apply physical models of buildings to impress immediate manipulation. Hands-on interaction lets city planners intuitively explore complex environmental simulations; because of the immediate way one can manipulate the models, this transforms views of shadows, airflow, and reflections, enhancing spatial reasoning and nurturing collaborative decision-making. The DataTiles system merges physical tiles with graphical user interfaces to support manipulations of digital information. Each tile encapsulates either a function or a dataset; hence, complex data operations can be done in a very natural and intuitive manner when a user physically arranges and combines these tiles across the tabletop interface. This reduces cognitive load due to the hands-on approach taken as opposed to the abstract handling of data and further manifest aspects of embodied cognition whereby spatial and physical engagement is undertaken to make sense of such complicated information.

These case studies have pointed out how, through tangible representation and real-time feedback, TUIs reduce cognitive load and enable deeper interaction. In either educational or technical training, or even exploratory creative activity, TUIs allow more ways of interacting with content digitally than uniquely possible with its capabilities beyond simple GUIs.

3. The accessibility and scalability of TUI

Arguably, scalability and accessibility can be said to be one of the grand challenges for mass adoption of TUIs. Here, scalability refers to their applicability for large amounts of settings and contexts effectively, while accessibility concerns would deal with how such interfaces can make them usable for other kinds of users, including those with disabilities.

Although TUIs have tremendous promise for revolutionizing any paradigm of interaction in education, industry, and society more broadly, their cost, adaptability, and inclusivity must first be addressed to fully realize that potential.

3.1. Scalability of TUI

Issue of Scalability with TUI Implementation Common issues to scale with TUIs are that, by their definition, they depend on physical objects, often very particular sensors, and real-time feedback mechanisms that are extremely expensive to manufacture and maintain. Such factors may decrease the potential to scale TUIs in terms of large-scale usage or deployment by institutions. Moreover, many TUIs are highly customized for specific applications or contexts in which they were developed, which basically makes it challenging to adapt them for usage in another situation pretty easily without significant re-engineering.

One of the main barriers to scalability is the added cost and complexity that TUI hardware brings: many TUIs call for unique physical objects, sensors, and actuators-all tightly integrated with digital systems. Such a thing makes replication at scale of TUIs harder than it is for their GUI counterparts, which require little more than commodity hardware in the form of keyboards and screens. To reach wider audiences with such components, innovation in materials and manufacturing technologies will be required to drive the cost down.

Sometimes, these TUIs are designed for quite specific tasks, like architectural model manipulation or training of surgical tools for medical students. More demanding challenges, however, occur when such highly domain-specific systems are adapted to general usage since interaction mechanisms will be tailored to fit a certain domain. Hopefully, modular and flexible development in TUI construction will overcome this limit in the future, whereby the ease of system design for different tasks or contexts should be easily possible.

3.2. Accessibility of interaction in TUI

Another major challenge is making TUIs accessible to a wider range of users, such as those with various types of impairments. Most of the TUIs would mean physical manipulation of objects, handling instruments, or gestures excluding people with various types of physical impairments; so, questions of accessibility are usually connected with the physical nature of TUIs. Very often, visual or hearing impairments make users face problems while working with TUIs dependent on sight or hearing.

For example, the design of systems for various abilities may make TUIs more usable. An example would be the design of tactile feedback systems for the visually impaired, which would allow them to touch the digital content instead of seeing visual cues. TUIs can also be designed with multimodal interaction capabilities: a user could be given a choice among various alternatives, such as visual, auditory, or even haptic feedback, whichever desired.

Some TUIs, on the other hand, design systems for persons with disability as a complement to alternative methods of interaction. In special education, for example, the Reach & Match Learning Kit teaches visually and motor-impaired children how to learn about cognition and social interaction through fiddling toys. In this case, the system features tiles and shapes that are easy to hold by a child and, as such, practical even for kids who cannot use most learning paraphernalia.

4. Applications of TUI

4.1. TUI in cognitive ergonomic

Cognitive ergonomics means improving systems and interfaces with respect to human cognitive skills, like perception, memory, and problemsolving. It hence means the objectives are minimal mental workload and maximum performance through user interfaces that are as natural as possible and intuitive use of technology.

Of these, TUIs hold the greatest promise because they allow physical and manual interaction with digital systems similar in naturalness to how people cognitively learn through sensemaking and motor activities. TUIs reduce cognitive load and enhance memory retention; they are greatly beneficial to both novices and experts in almost any domain. TUIs are crucial in cognitive ergonomic media for filling the chasm between the digital information and the physical interaction. It allows the manipulation of content found in a digital component using tangible objects, fitting human behavior, besides minimizing abstract thinking developed through more common GUIs. Such physical manipulation intuitively simplifies complex tasks and reduces mental effort toward the execution of such tasks.

For instance, design applications can allow users to create physical components simultaneously represented in their digital form. That sort of direct manipulation reduces the number of steps in translating an idea into digital form in such a way that efficiency and user satisfaction increase. By spreading cognitive load through externalization onto the physical environment, TUI allows for complex systems to be more accessible and understandable.

Research based on cognitive science suggests that TUIs actually reduce mental workload because the cognitive work is divided between a user and physical objects based on the concept of distributed cognition. In this model, cognition does not necessarily centralize to the brain but appears rather diffused throughout objects, tools, and interactions in an environment. TUIs follow the same principle with performing complex tasks in the form of physical interaction with manipulation of tangible objects controlling digital data. For example, instead of recalling abstract commands or navigating through complex menus, users can manipulate a real object that has direct relevance for the digital function to be performed.

Another relevant cognitive theory is embodied cognition, which suggests that thinking and problem-solving are situated in bodily interactions with the environment. TUIs will quite agree with this theory as it allows a user to physically interact with digital information. This reduction in the amount of cognitive effort also increases retention in memory while solving problems.

Research conducted by Marshall et al. has proven that users of tangible interfaces have low cognitive load, and their ability to remember things improves compared with people using the traditional GUIs [7]. This reduces mental effort makes TUIs a more cognitively ergonomic choice, especially in complicated tasks where users are meant to handle different flows of information at the same time.

4.2. TUI in education

TUI represents the changing landscape and the industry in education by using intuitive hands-on interaction with digital systems. In education, it fosters active learning whereby learners interact with manipulated physical objects to represent complex digital data, ideas, or systems to provide a more direct way of grasping abstract ideas.

They have greatly enhanced the productivity and innovation in those areas of design, engineering, and medicine where the hallmarks of effective problem solving and training were physical manipulations of data. The potential in reworking of practice in education lies with TUIs, setting the student within a virtual, interactive learning environment in a fully engaging way on many levels. Unlike the more conventionally based forms of education, using abstract symbols and screen-based interactions, TUIs allow the use of a person's hands and their physical intuition to explore and interact with concepts directly.

These learning spaces will be very effective for lessons on technical and scientific subjects. Mechanisms like the Topobo, a tangible 3D construction kit developed at MIT, enables students to make dynamic constructions and investigate principles of mechanics and biology [8], let students learn about the abstract concept of forces, motion and balance more concretely, by combining pieces and observing the physical result.

An involvement based on practice in reality gains much higher retention capabilities and understanding compared to theoretical approaches based purely on lectures and textbooks. For example, the Tangible Math Project draws on concrete objects or manipulatives, such as blocks or shapes, to introduce mathematical concepts [9]. These can demonstrate addition and subtraction or multiplication in a manner that the abstract problems can be represented concretely when arranged horizontally or vertically. Research evidence shows that tangible interfaces do improve cognitive processing and retention better than those using paper input, with students also forming a more conceptual view of math ideas.

TUIs also support collaborative learning within group activities by getting different students to manipulate physical objects. An example involves a musical instrument called Reactable, which is mainly an object controller for sound and music generation, adopted in some school settings to teach sound waves and frequency. This enhances the working together of students toward goals based on teamwork and interaction.

4.3. TUI in industrial applications

TUIs in industrial environments have become essential features that improve the workflow, encourage creative work, and assist in the optimization of training. From product design to medical training, TUIs will give professionals a much more natural way of interacting with complicated digital systems and provide a perfect mix of physical manipulation and digital feedback. TUIs do even more in generating a design dynamically related to architecture, engineering, and industrial design. For instance, Urp can be considered a tangible interface for urban planning. This lets architects and city planners manipulate physical building models and see immediate digital sim­ulations showing them sunlight, shadow, and airflow. The interaction provides immediate feedback that allows designers to make more informed decisions and accelerates the creative process while increasing accuracy.

TUIs have been most useful in medical training, which requires practical exposure to develop the so-called technical skills. A classic example is surgical simulators, which are TUIs; for instance, the LapSim simulator includes a realistic imitation of the feel of real surgical instruments for laparoscopic surgery [10]. They can further practice as much as they need in a no-risk-of-complication controlled environment. These physical simulations are proven through research to enhance skill acquisition and retention compared to a traditional screen-based simulation.

They also find their applications within smart factory environments in manufacturing, simply operating by enabling workers to use tangibles for the control of robots and automated systems to thereby make immediate changes in the line of production. A direct manual interaction with machines enhances operational efficiency and reduces the complexity in managing automated systems.

It enables engineers, for example, at car manufacturing, to handle physical prototypes of parts while analyzing the result of such changes in virtual simulation, hence fastening the design and manufacturing process.

4.4. TUI applied to the concept of the internet of things

IoT has only begun to radically change how people relate to their surroundings by connecting 'inanimate' objects to the digital world. Needless to say, TUI is an extension of that concept as it grants users the ability to manipulate and interact with the linked systems through physical artifacts. When TUIs are introduced into the IoT, by default, they become a partner in the infusion of the physical and digital worlds, thereby making possible easier, intuitive, and more effective smart systems.

However, that is not all because TUI increases the degree of direct interaction between the user and real objects, with this coupled by an increase in accessibility and improvement in user autonomy in IoT ecosystems. That may allow new, revolutionary interactions to emerge for smart homes and wearables to industrial automation and urban infrastructure.

4.4.1. Improving tangibility and control This would be of immense benefit for IoT systems due to usability and accessibility, with the additional advantage of physical interfaces providing intuitively controlled forms of handling connected devices. Traditional approaches to the handling of IoT systems have undergone controls through screen-based control or mobile apps that normally become a tasking to work with and get the user disconnected from the physical environment. TUIs entail a more direct and tangible aspect of interaction, making them closer to human cognitive and sensory processes.

It would be the interface from which various devices in smart homes could be controlled, including, but not limited to, lights, temperature and security systems. For example, it would turn the real-world dial or slider to control your light or the temperature of a room so getting out of complicated applications or memorizing voice commands is superfluous in achieving intuitive and attractive interaction.

For one, people can appreciate such immediate, tactile feedback through vibration or click, increasing their sense of mastery of their surroundings.

Another significant component of IoT that may be coupled with TUI is the wearable device. Wearable devices might contain physical controls like buttons or sliders, and may even contain sensors that can sense hand gestures; users would not need to glance at screens or use their voice. This makes the user experience even more natural and intuitive -- particularly among individuals whose activities would be disrupted in any particular way by having to look down at a phone or screen, such as exercise or driving.

4.4.2. Industrial integration with the internet of things This is the area where TUIs can really make a difference in industrial environments to make IoT-enabled environments efficient and safe. As more IoT technologies keep appearing within manufacturing, logistics, and urban infrastructure, there is an expectation that the need for a new typology of interaction may be required, allowing workers to control and manage complex systems in screenless and cursorless ways.

TUIs are more useful in industrial settings because they require one to operate directly physically with the machines. The idea here is that in factory automation, one may consider using tangible interfaces to create controls of the robot or some kind of automated system. Workers will manipulate the physical object-levers, buttons, or dials linked to specific machine functionality enable real-time adjustments and monitoring. This improves operational efficiency and reduces the cognitive burden toward managing such complex systems via abstract software interfaces.

For example, it may enable an even stronger interaction with smart urban infrastructure, such as traffic control or public transportation networks and energy grids. Through the use of a physical model of city layouts, planners or operators can manipulate and visualize data where decisions based on flow, energy consumption, or emergency responses are intuitively embedded into physical interaction.

5. Problems and limitations of TUI as method of interaction

5.1. Overcoming technical complexity and high development costs in TUIs

The reason behind increased development cost, however, also deals with technical complexity, since TUI demands sophisticated technology in order to merge the physical world and digital systems smoothly. Such TUIs do require sensors, actuators, and specialized software to create real-time feedback with precise spatial interaction. Higher technical demands, therefore, increase the development cost compared to traditional GUIs, which makes the TUI rather less accessible for small projects or institutions with limited budgets.

This financial barrier thus blocks the wide-scale implementation of TUIs in educational or research settings where these unique affordances would be maximally utilized. To overcome these barriers, researchers and designers are opting for open-source hardware and software components that are affordable and modular which help reduce the cost of designing TUIs and lower the entrance barrier [11].

5.2. Overcoming user resistance and making the learning curve smooth in TUI

Users who are used to the old traditional GUI may also resent being migrated onto TUI simply because of a very new and different interaction paradigm. In TUI, this relies on manipulation and spatial interaction. To users who are used to a pointing device, their work may be less intuitive at first while working with tangibles. Such increased friction could result in decreased satisfaction and overall task efficiency if, for instance, the interface is not well designed or has very few affordances.

Another source of frustration could be the unknown style of interaction, which might, on the other hand, also bound the role of the TUIs within a given context. Gradual integration strategies, such as hybrid interfaces integrating GUIs and TUIs, help in gentle switching. Full users' education and intuitive design-like clear visual clues and affordances-will contribute to smoothing the path through such challenges. 5.3 Overcoming Environmental and Contextual Obstacles in Deploying TUIs

The physical space requirements and environmental limitations can be the bottlenecks with which TUIs may have to deal. For instance, TUIs dependent on wide spatial interaction might just not come in handy in a small or crowded environment. These environmental liabilities of usability are major liabilities in the usability of TUIs, making it not practical in scenarios when space becomes a premium, or where tight and exact physical interaction is constrained by elements such as illumination or noise conditions. It is within such bounds that the development of TUIs in smaller scales, reducing the need for physical space, and further exploring the use of extensions of tangible interfaces-such as virtual or augmented reality-allows TUIs to run under suboptimal conditions while retaining their full benefits.

6. Conclusion

This is indeed one of the revolutionary ways in which humans interact with computers, as that helps to bridge gaps-both physical and digital-in a much more natural and intuitive way. With this in place, the paper was able to assert the potency of TUIs to result in considerable cognitive advantages, particularly on reducing cognitive load and improving memory retention, which conformed to distributed and embodied cognition theories. Cognitive ergonomics, education, and industrial applications make TUIs versatile and effective in enabling the accomplishment of complex tasks, collaborative learning, and workflow efficiencies. With so much disadvantage at the onset of the adoption of TUIs, the list including but not limited to technical complexities, expensive development costs, and resistance by users owing to a shift from their known graphical user interfaces, truly innovative solutions such as affordable and modular components of TUIs, hybridized interfaces combining TUIs and GUIs, and intense education for the user to relieve the transition must be done. It will also integrate the concept of the Internet of Things for better connectivity and control in smart environments-from smart homes to industrial automation. This growth of TUI will, thus, enable an improved promotion of multisensory and embodied interaction and, therefore, further fuel innovation in HCI in order to make digital interactions smooth and compatible with human cognition and senses.

Generally speaking, whereas TUIs are ahead with advantages than the traditional interfaces, their success might just as well be reviving from how far the scalability and accessibility barriers are overcome. For TUIs to fully realize their potential for better, more intuitive, efficient, and engaging human-computer interfaces, more research and development, besides careful design and implementation strategies, would be needed.